It is hence clear that the [Greek: b]-sulphonic acid possesses phlobaphene-solubilising qualities greater than those of the [Greek: a]-sulphonic acid or the disulphonic acid; the Greek: b]-sulphonic acid was therefore made the subject of Ger. Pat., 181,288 (8th February 1917).

The synthetic tannin, Ordoval G, is the formaldehyde condensation product of higher hydrocarbons (mainly retenes), and is a partly neutralised product containing no sulphuric acid. The author's analysis gave the following figures:—

Tanning matters 10.7 per cent. Soluble non-tannins 16.4 " Insolubles 0.0 " Water 73.0 "

Acidity: 1 gm. = 4 c.c. N/10 NaOH. Density: 23 Be.

Ordoval G is completely soluble in water and glacial acetic acid. Only its organic constituents are soluble in alcohol, ethyl acetate, and acetone, whereby a dark coloured crystalline mass separates. Ordoval G is insoluble in benzene.

The aqueous solution of Ordoval G gives the following reactions:—

Gelatine Moderate flocculent precipitate. Ferric chloride Darkish coloration. Potassium dichromate No reaction. Aniline hydrochloride Dark brown precipitate. Formaldehyde hydrochloric acid No precipitate. Bromine water No reaction. Zinc acetate Very slight opalescence. Barium chloride Slight opalescence.

Its capability of solubilising and consequent saving of natural tannins is shown by the fact that 100 kilos of vegetable tanning material may be substituted by 40 kilos of Ordoval G and the material in question in order to obtain the entire tanning intensity of the latter.

In one respect—that of its salts—Ordoval G differs from the Neradols; whereas the chromium and aluminium salts of the latter possess no such tannoid properties as will make the resultant leather exhibit any of the characteristics of either tannage, it is possible to carry out combined tannage with a mixture of Ordoval G and metallic salts. Tanning experiments carried out with the chromium, iron, aluminium, and calcium salts of Ordoval G yielded leathers which possessed proportionate characteristics of either kind of tannage to the extent to which either material was present. This combination tannage seems to be assured of a great future; especially may a combination tannage of iron salts and Ordoval G eventually entirely replace chrome tannage.

The detection of Ordoval G in leather is carried out as follows: 10 gm. of leather are boiled with 150 c.c. of acetic acid, a solution of 25 gm. of CrO_8 in 25 c.c. of a 50 per cent, solution of acetic acid gradually added, and the mixture boiled for three hours, till the leather is decomposed and the solution has assumed a brown instead of the original light yellow colour. The solution is then evaporated, the residue dissolved in 600 c.c. hot water, and the chromium precipitated with a 40 B. solution of caustic soda. The solution is filtered and cooled, and a little hydrosulphite is added to 20 c.c. of the cold alkaline filtrate; in the presence of Ordoval G, a red colour will appear (oxanthranolsulphonic acid).

Brief mention must be made of the so-called Corinal [Footnote: Swiss Pat, 78,282, 78,797, 79,39.] a synthetic tannin placed upon the market by Chem. Fabrik Worms A.-G., in Worms-on-the-Rhine. It is a viscous, brown fluid, containing the aluminium salts of the tannoid acids. The latter are formaldehyde-condensation products of sulphonated tar oils, or the hydroxylated derivatives of the latter. The density being 33 B, it contains 28.1 per cent. tanning matters, 13 per cent. soluble non-tannins, and 10.8 per cent. inorganic matter (3.2 per cent. Al2O3 and 7.6 per cent. Na2SO4.

A similar product, containing chrome salts as base, is the so-called ESCO-EXTRACT, [Footnote: Schorlemmer, _Collegium_, 1917, 124] manufactured by the Chem. Fabrik Jucker & Co. in Haltingen (Baden). This product is a dark, reddish-brown fluid, possessing acid reaction, which strongly precipitates gelatine. Analysed by the filter method it contains 12-15 per cent. tanning matters, 17-20 per cent. soluble non-tannins, and 18 per cent. ash, of which 3 per cent. is Cr2O_3. This synthetic tannin may be employed alone or in conjunction with other tannins, and yields a leather similar to that obtained by chrome tannage.

A. Condensation of Free Phenolsulphonic Acid

In practice, the results of condensing phenolsulphonic acid with formaldehyde are manifold, according to whether these materials are used in their concentrated or dilute state; whether they interact in the cold or when heated; or whether their interaction is gradual or rapid.

1. If a moderately dilute solution of phenolsulphonic acid (1:1) is mixed with one-sixth of its volume of a dilute formaldehyde solution (1 part 30 per cent. HCHO solution plus 3 parts of water) in the cold, with continuous stirring, the solution remains clear and assumes a brown colour. When left several hours, a light, white flocculent precipitate deposits, which increases in quantity on diluting with water. The solution precipitates gelatine; the flocculent precipitate is easily soluble in hot caustic soda solution, and, when subsequently neutralised with acetic acid, precipitates gelatine.

If equal parts of dilute phenolsulphonic acid and dilute formaldehyde (concentrations as above) are gradually mixed in the cold, whilst stirring, the mixture soon becomes opalescent, and a flocculent deposit separates after eighteen to twenty-four hours.

These experiments carried out on the water bath immediately yield opalescent liquids, from which an insoluble, brown, gluey, and very sticky mass separates after twenty-four hours; the latter is sparingly soluble in alkalies, partly so in organic solvents.

2. If a moderately dilute solution of phenolsulphonic acid (1:1) is gradually mixed with one-sixth of its volume of a concentrated (30 per cent.) formaldehyde solution in the cold, whilst stirring, slight opalescence immediately results, and a flocculent deposit separates after about twenty minutes, which gradually increases in quantity during the next few hours. If the volume of formaldehyde is increased to the same as that of phenolsulphonic acid solution, the flocculent deposit immediately separates, and after twenty-four hours a brown, gluey, and very sticky mass—of the same solubility as that described in the previous experiment—is to be found at the bottom of the vessel used.

It should be noted that in both these experiments with concentrated formaldehyde solution a slight increase in temperature occurs concurrently with the process of condensation. If the experiments are carried out on the water bath, a gelatinous mass is instantly formed, which assumes the colours of grey, dirty light violet and dark violet, in the order named, and which, whilst left several hours—or when heated on the water bath—is suddenly converted into the insoluble, brown, gluey mass above referred to.

3. If, for the purpose of condensation, phenolsulphonic acid to which 10 per cent, of water has been added, is employed, the reaction proceeds very quickly and energetically. If one-sixth of its volume of formaldehyde (1:3 of the 30 per cent. solution) is added drop by drop to a cold solution of phenolsulphonic acid, a reddish, milky solution results, which assumes a slightly lighter colour on addition of more formaldehyde and deposits an insoluble flocculent precipitate. If the solution is kept below 45 C., by artificial cooling, the light colour is maintained, but a gelatinous precipitate is soon formed, the viscosity of which increases on stirring, and finally is converted into an insoluble, tough, gummy mass. If, on the other hand, the mass is heated at the beginning of the reaction, or if the amount of formaldehyde is increased and the mass cooled during reaction, effervescence occurs, and a cheesy, dirty-coloured mass results, which, on cooling, rapidly becomes solid and yields a very firm, elastic, rubbery mass, which is absolutely insoluble in water.

4. The condensation proceeds exceedingly violently when concentrated phenolsulphonic acid is acted upon by one-sixth of its volume of formaldehyde. If the latter is firstly added drop by drop to the phenolsulphonic acid, a gel immediately results, the temperature of which quickly increases on further addition of formaldehyde and suddenly boils over, yielding a reaction product which, when cooled, forms a dirty violet, firm, elastic, and rubbery mass, insoluble in alkalies and hardly affected by organic solvents.

Finally, if the amounts of concentrated phenolsulphonic acid and formaldehyde stated above are mixed, strong effervescence occurs and heat is evolved, and a dirty blackish-violet mass is instantly formed which, on cooling, yields a rather brittle, hard product insoluble in water.

5. Totally different end-products are, however, obtained when the addition of formaldehyde (30 per cent.) in the proportion of one-sixth of the volume of dilute phenolsulphonic acid (1 plus 9 aq.) to the latter is extended over several hours. In this case a slightly opalescent liquid is obtained which, when left twelve hours, is transformed into a brown mass soluble in water, which strongly precipitates gelatine and possesses tanning properties. Hence direct tannoid substances are obtained by this method of condensation.

Whereas no direct tanning experiment can be carried out with the insoluble compact mass obtained in the preparations described above on account of their absolute insolubility, it is still possible to carry out tanning experiments with opalescent colloidal solutions in the following ways:—

(a) If a bated pelt is immersed in a liquid containing a condensation product obtained by gradually mixing a moderately dilute solution of phenolsulphonic acid and a dilute solution of formaldehyde, the pelt is rapidly tanned on the surface. Complete penetration of the substance does not occur even after several days, since the strong acidity of the solution causes a strong swelling of the pelt.

(b) If a pelt is shaken for six hours in a shaking apparatus containing the liquid mentioned under (a), tannage again only takes place on the surface, penetration being impeded by the strong swelling effect of the liquid. Repetition of the latter two experiments, with the addition of 15 per cent, common salt, increases the tanning effect to some extent; the pelt, however, is not tanned through, but the non-tanned layers may be clearly seen to be pickled.

The tanning effects described above are only exhibited when the colloidal tan-liquor is present in great excess over the pelt, since the former obviously only contains small amounts of tanning matter, and even the presence of common salt does not bring about complete tannage of the pelt.

In order to prove the presence of "tanning matters" in the liquid described above, several freshly prepared samples of the latter were analysed by the shake method of analysis without being first filtered and the following figures obtained:—

1. 2. 3. 4. Per Cent. Per Cent. Per Cent. Per Cent. Tanning matters 6.4 7.7 8.2 9.1

Soluble non-tannins 15.2 17.4 14.5 11.8

These condensation products suspended in water all precipitate gelatine strongly and leave behind a perfectly clear liquid. In all cases, an intense blue colour was obtained on adding ferric chloride, a slight precipitate only was obtained with aniline hydrochloride, and bromine was rapidly absorbed with the separation of an insoluble white deposit.

The condensation products obtained by the interaction of dilute solutions of phenolsulphonic acid and formaldehyde at moderately high temperature, which form slimy masses and are insoluble in water, are soluble in alcohol. An alcoholic solution of such a product was used in a tanning experiment, and a piece of pelt immersed in the solution was tanned through in a few days; the resultant leather being rather firm, springy, and slightly hard, and the colour was a light brownish-grey.

All those condensation products which are easily or partly soluble in alcohol dissolve in caustic soda, sodium carbonate, in some cases also in borax and sodium sulphite. They are rendered soluble with greater ease when the freshly prepared solution is heated on the water bath with the alkali; the alkaline solution, neutralised as far as is possible with acetic acid, yields light brown coloured solutions, the tanning effects of which have proved very satisfactory. Leathers tanned in such solutions, however, are rather empty and hard, possess but little resilience and an uneven, dirty greyish-brown colour.

A sample of such a product, as nearly as possible neutralised with acetic acid, contained 14.8 per cent. tanning matters, by the shake method of analysis.

B. Condensation of Partly Neutralised Phenolsulphonic Acid

Attempts were made at condensing partly neutralised phenolsulphonic acid; the latter was obtained by mixing equal quantities of phenolsulphonic acid and sodium phenolsulphonate (prepared by exactly neutralising phenolsulphonic acid with a concentrated solution of caustic soda).

The consequent dilution and decrease in acidity, however, considerably diminished the velocity of the reaction. Hence, if the half-neutralised Solution A1 (cf. p. 98) is diluted with water, taking equal volumes, and one-sixth of the volume of dilute formaldehyde (1:3) gradually added in the cold, condensation is not induced. When heated several hours an opalescent liquid results from which, however, no flocculent deposits separate when left for some time. Using a concentrated solution of formaldehyde (Experiment A2, p. 98) in the cold produces no reaction, but after heating for a time an opalescent liquid is obtained. Both liquids give only slight precipitates with gelatine. Excess formaldehyde does not influence the reaction.

A repetition of Experiment A3 (cf. p. 99), using the above half-neutralised phenolsulphonic acid, similarly required heat to induce condensation, when a milky liquid of light reddish colour resulted.

Whereas the addition of formaldehyde to non-neutralised concentrated phenolsulphonic acid caused violent reaction, this proceeded very slowly in the case of half-neutralised phenolsulphonic acid, resulting in the formation of a semi-solid mass, which on heating became more viscous, and finally, when left twenty-four hours, became a solid, compact, insoluble mass possessing a dirty light violet colour.

Tanning experiments with these opalescent solutions proved them to exert a rapid penetration on the surface, complete tannage, however, taking place after eight days only, when a flat, greyish-coloured and rather hard leather resulted.

C. Condensation of Completely Neutralised Phenolsulphonic Acid

If concentrated phenolsulphonic acid is gradually neutralised with concentrated caustic soda solution till the former is faintly alkaline, the sodium salt thus obtained is not so easily condensed with formaldehyde as is the case with the free acid.

1. If formaldehyde is gradually added to the neutralised phenolsulphonic acid in the cold, opalescence immediately results; on addition of water, the liquid assumes a milky appearance. On adding gelatine to this liquid, a slimy precipitate is thrown down, leaving a slightly opalescent liquid.

2. If formaldehyde is added to neutralised phenolsulphonic acid whilst it is heated on the water bath, a slimy mass instantly separates, which on cooling solidifies and forms a greyish-blue brittle mass, insoluble in water and but sparingly soluble in alcohol; the alcoholic solution is capable of converting pelt into leather.

The filtrate from the solidified mass strongly precipitates gelatine, whereas the insoluble condensation product is soluble in caustic soda; this alkaline solution also precipitates gelatine and the addition of acetic acid transforms the mixture into the gel state.

If the insoluble condensation product is dissolved in warm concentrated sulphuric acid, the solution remains clear upon the addition of water, but does not precipitate gelatine. If, finally, this solution is neutralised with caustic soda, the solution remains clear and precipitates gelatine strongly.

D. Condensation of Cresolsulphonic Acid

Experiments were carried out with the object of condensing o-, m-, and p-cresolsulphonic acids with formaldehyde in various ways; no essential differences could be detected as regards the mode of reaction or the properties of the intermediary and end-products as compared to those of phenolsulphonic acid. Similarly, condensation of different samples of crude cresol containing varying quantities of o-, m-, and p-cresol did not yield end-products sufficiently different to justify describing them in detail.

E. Relative Behaviour of an Alkaline Solution of Bakelite and Natural Tannins

Phenolsulphonic acid was condensed with a little formaldehyde, and the reddish pasty condensation product dissolved in caustic soda. This alkaline solution of bakelite was exactly neutralised with acetic acid and mixed with strong solutions of an untreated quebracho extract. It was observed that the solubility of the quebracho extract was not increased by this treatment, but the faintly acidic character of the natural tannin caused the bakelite to be thrown down as an insoluble precipitate.

Crude phenolsulphonic acid, when added to a solution of the quebracho extract referred to, does not increase the solubility of the latter, which even deposits considerable amounts of insoluble tannin particles.

Quite different properties are exhibited by sodium phenolsulphonate, which completely converts quebracho tannin into a water-soluble substance, the aqueous solution of which deposits no insolubles. The partly neutralised condensation product of phenolsulphonic acid and formaldehyde exhibits similar properties [Footnote: Grasser, Collegium, 1913, 521, 478.] (see later).

F. Dicresylmethanedisulphonic Acid (Neradol D) [Footnote: Ger, Pat., 291, 457; Austr. Pat., 61, 057.]

Neradol D is a viscous liquid, measuring about 33 B., which is similar to extracts of natural tannins. One of its characteristics is its phenolic odour; it is completely soluble in water, forming a clear, semi-colloidal solution, but is insoluble in all organic solvents with the exception of alcohol, glacial acetic acid and ethyl acetate, which dissolve all but its inorganic constituents. The latter owe their presence to the neutralisation of the crude Neradol with caustic soda, and are composed of sodium salts of the sulphonic acid in addition to Glauber salts.

The aqueous solution of Neradol D shows properties similar to those exhibited by solutions of natural tannins and reacts as follows:—[Footnote: Grasser, Collegium, 1913, 520, 413.]

Methyl orange Acid reaction. Barium chloride White precipitate, insoluble in HNO_3. Ferric chloride Deep blue coloration. Silver nitrate Slight opalescence. Bromine water No precipitate. Formaldehyde hydrochloric acid No precipitate. Gelatine Complete precipitation. Aniline hydrochloride Strong precipitate.

The reactions with ferric chloride and gelatine should be especially noted, since they are analogous to those given by natural tannins. On the other hand, the reactions with BaCl_2, bromine water and formaldehyde hydrochloric [Footnote: Stiasny carries out the reaction with formaldehyde-hydrochloric acid as follows:—50 c.c. of the tannin solution, plus 5 c.c. concentrated hydrochloric acid and 10 c.c. formaldehyde (40 per cent.) are heated under reflux condenser for ten minutes; most natural tannins are completely precipitated (_Collegium_, 1906, 435; 1907, 52 _et_ 188).] acid prove the different chemical composition of Neradol D as compared to that of the natural tannins.

The fact that a positive reaction is given with aniline hydrochloride [Footnote: This reaction is carried out as follows:—5 c.c. of the tannin solution to be examined (about 4 gm. tanning matter per litre) are shaken violently in a test tube with 0.5 c.c. aniline and 2 c.c. concentrated HCl added. All natural tannins are unaffected by this treatment, ligninsulphonic and other sulphonic acids cause opalescence. Note.—Employing formic acid in lieu of hydrochloric acid (Knowles) renders the reaction no more reliable.—Transl.] is very puzzling; none of the natural tannins are precipitated by this reagent, but only sulphite cellulose on account of its content of ligninsulphonic acid. One is justified in assuming that there is at least some connection between the constitution of ligninsulphonic acid and that of dicresylmethanedisulphonic acid.

Stiasny [Footnote: Collegium, 1913, 516, 142.] recommends the following reaction for the detection of and differentiation between Neradol D and wood pulp extract:—10 c.c. of a 5 per cent. solution of the extract to be analysed are violently shaken with 1-2 drops of a 1 per cent. alum solution and about 5 gm. of ammonium acetate. If only Neradol D is present no precipitate separates even after twenty-four hours, but if wood pulp be present, a precipitate is thrown down in a quantity corresponding to the amount of wood pulp present.

The official analysis gives the following figures: [Footnote: Grasser, loc. cit.]

Tanning matters 32.5 per cent. Soluble non-tannins 33.0 " Insolubles 0.0 " Water 34.5 " ——————- 100.0 per cent.

Ash 17.0 "

Acidity: 1 gm. = 10 c.c. N/10 NaOH. Density: 33 B.

A comparison of its quantitative analysis to that of a natural tanning extract is illustrated by the following figures of a chestnut and a quebracho extract of same density (26 B):—

Chestnut Quebracho Per Cent. Per Cent. Tanning matters 32.0 34.0 Soluble non-tannins 12.0 8.0 Insolubles 1.5 2.0 Water 54.5 56.0 ——- ——- 100.0 100.0

Ash 0.4 2.0

This comparison shows that extracts of natural tannins firstly contain certain amounts of "insolubles," whereas Neradol is completely soluble in water, forming a clear solution; secondly, natural tanning extracts contain smaller quantities of soluble non-tannins, consisting of colouring matter and sugars, in addition to small quantities of mineral matters (ash). Neradol D contains considerable amounts of soluble non-tannins, derived from salts of sulphonic and sulphuric acids, again offering a satisfactory explanation of the high ash. If, therefore, a mixture of Neradol D and a natural tanning extract was submitted to a quantitative analysis, the higher non-tannins and the high ash would indicate the presence of Neradol D, provided that wood pulp or a highly sulphited extract were not components of the mixture.

The chemical reactions taking place in the preparation of Neradol D may be expressed thus:-

OH OH OH OH H ^ HOH ^ H H ^ HCH2H ^ H = + H2O CH2 H v CH3 CH3 v H v CH3 CH3 v H HSO3 HSO3 HSO3 HSO3



1. Neradol D Reactions

1. The quantitative determination of phenols introduced by Bader, [Footnote: Bull. soc. scient., Bucarexi, 1899, 8, 51.] which consists in precipitating them as oxyazo compounds, has been modified by Appelius and Schmidt [FootNote: Collegium, 1914, 597.] for the purpose of detecting Neradol D:—To 50 c.c. of the tannin solution (analytical strength) 15 c.c. of diazo solution are added, the mixture filtered, if necessary, and the filtrate made alkaline with caustic soda; in the presence of Neradol D in sufficient quantity, a blood-red coloration results. If but little Neradol D be present, the procedure is altered as follows:—The tannin solution, to which the diazo solution has been added, is filtered, and the filtrate poured on a piece of filter paper which is then dried; a solution of caustic soda is spotted on the paper, when, if Neradol D be present, a red-edged spot will appear.

According to Tschirch and Edner, [Footnote: Archiv. d. Pharm., 1907, 150.] the diazo solution is prepared as follows:—5 gm.p-nitraniline are introduced into a 500 c.c. measuring flask, 25 c.c. of water and 6 c.c. concentrated sulphuric acid added, the mixture shaken and a solution of 3 gm. of sodium nitrite in 25 c.c. of water plus 100 c.c. of water added, and the whole then filled up to 500 c.c. The solution should be stocked in the dark.

2. A less sensitive reaction for Neradol and wood pulp extract constitutes that of Appelius and Schmidt employing cinchonine, [Footnote: Collegium 1914, 597.] while the presence of the substances in question yields characteristic precipitates.

3. Seel and Sander [Footnote: Zeits. f. ang. Chem., 1916, 333.] recommend the following method of detecting Neradol D:—

(a) Oxyazo Reaction.—About 5 c.c. of the tannin solution are rendered alkaline with caustic soda; after cooling with ice, about half the volume of alcohol is added. 3-4 drops of diazo solution are then added. Frequently, this results in the solution assuming a blue coloration. If not, the solution is acidified with hydrochloric acid, ether added, and the mixture well shaken. The water is now separated from the mixture, fresh water added, together with some caustic soda solution, when, if Neradol D be present, the salt of the colour acid formed dissolves in the water with a beautiful green or bluish-green colour. At the place of contact of the water and the ether a bluish-green ring appears.

The diazo solution is prepared by dissolving p-aminophenol or its hydrochloric in a little dilute hydrochloric acid, cooling in ice and carefully diazotising in the cold till a slight excess of nitrous acid is present. It is essential that this solution should be tested before use, and this is carried out by coupling it with an alkaline phenol solution; if a dark blue oxyazo colour is formed, the solution may be used. It must be kept cool by surrounding it with ice.

(b) Indophenol Reaction.—To 5 c.c. of the solution to be tested, a drop of a solution of dimethyl-p-phenylenediamine is added, the solution rendered alkaline with caustic soda and 1-2 drops of a 5 per cent. solution of potassium ferricyanide added. If Neradol D be present, a blue colour appears, either immediately or after some time. The reaction is rendered more sensitive if alcohol is carefully poured on the solution after it has been rendered alkaline, and potassium ferricyanide is then added. At the place of contact a blue layer is formed, which ultimately diffuses into the alcohol.

According to Lauffmann [Footnote: Collegium, 1917, 233.] the presence of natural tannins as well as that of wood pulp diminishes the sensitiveness of the reactions described above; [Footnote: Zeits. f. ang. Chem., 1916, 333.] this investigator recommends a modification of these reactions.

2. Electro-Chemical Behaviour of Neradol D

The author's investigations of the electro-osmosis of an aqueous solution of Neradol D [Footnote: Collegium, 1920, 597, 24.] proved that dicresylmethanedisulphonic acid exhibits anodic migration; hence this product possesses negative charge and acidic character. The impurities accompanying the synthetic tannin, i.e., salts, free sulphuric acid, and some phenols, migrated anodic and cathodic respectively, according to their charges. A Neradol D purified by electro-osmosis finally yielded a pure solution of dicresylmethanedisulphonic acid, which precipitated gelatine and exhibited pronounced tanning effects, but gave a greenish-black coloration with iron salts. This conclusively proves that the blue coloration given by Neradol D with iron salts is no characteristic feature of the pure synthetic tannin, but is caused by the phenolic impurities accompanying the latter. Especially the first stage of the electro-osmosis produces a cathodic migration of the phenols, which may then be detected at a cathode by means of the iron and bromine reactions.

It is characteristic of a dicresylmethanedisulphonic acid purified by electro-osmosis that it does not precipitate aniline hydrochloride. It appears, therefore, that this reaction—which is characteristic of most synthetic tannins—is again caused by the presence of impurities.

3. The Influence of Salts and Acid Contents on the Tanning Effect of Neradol D

Chemical analysis of crude Neradol revealed a natural dicresylmethanedisulphonic acid (the tanning agent) contents of about 68 per cent, which agrees fairly well with the calculated amount. Like other "strong" and "weak" acids this sulphonic acid exercises a strongly swelling influence on pelt. Whereas the effect of acid present in solutions of Neradol D of medium concentration and its tanning effect both influence the pelt and are fairly well balanced, this is not the case as regards highly concentrated and very dilute solutions. If, for instance, a very dilute solution of crude Neradol (about 0.25 B.) is used, the tanning effect of this solution is exceedingly small and does not show itself till after several hours. The relatively high dissociation of the acids at this high degree of dilution causes an extremely rapid and strong swelling of the pelt, which has therefore absorbed its maximum amount of water (maximum swelling) before the tanning effect of the sulphonic acid comes into play and by fixing the surface of the pelt is enabled to prevent the excessive swelling effect of the acids.

The addition of neutral salts to the tan liquor diminishes the effect of the acids on pelt (dehydrates the pelt) and prevents "drawing" of the grain. If, for instance, common salt be added to a solution of crude Neradol, the original quantity of sulphonic acid present would remain constant, but the presence of salt would diminish the degree of dissociation and consequently the swelling. This effect is still more pronounced when the absolute amount of free sulphonic acid is diminished. Hence, if crude Neradol is treated with increasing amounts of caustic soda, a series of products containing increasing quantities of salt and decreasing concentrations of sulphonic acid is obtained.

The acidity of the Neradols may be determined by titration with N/10 caustic soda; this procedure hence establishes a means of determining the (unknown) acidities which may be expressed in terms of c.c. N/10 NaOH. The acidity of crude Neradol was found to be—

1 gm. = 50 c.c. N/10 NaOH

i.e., 1 gm. of crude Neradol requires 50 c.c. N/10 NaOH for complete neutralisation; the decrease in acidity causes a decrease in contents of tanning matters and the quantities of salts increase. The following table gives the figures obtained by differently neutralised neradols:—

Acidity. Tanning Matters. Na2SO4.

Per Cent. Per Cent. 1 gm. = 50 c.c. 68 ... 1 gm. = 40 c.c. 59 4 1 gm. = 30 c.c. 50 8 1 gm. = 20 c.c. 41 12 1 gm. = 10 c.c. 33 17 1 gm. = 5 c.c. 28 20 1 gm. = 0 c.c. 20 ...

Tanning experiments with these different neradols (employing solutions of 1 B. strength) demonstrated that neradols of acidity 50, 40, and 30 exerted strong swelling and gave comparatively hard leathers; neradols of acidity 20, 10, and 5 exert no swelling, yield quick tannage and soft leather. The swelling (hardening) effect of the acid and the dehydrating (softening) effect of the salts in this case, therefore, are well balanced, and this fact affords an explanation of the rapid change from hardening to softening effects exhibited by partly neutralised Neradol where less acid and a greater quantity of salts respectively are present.

It may finally be noted that the acidity of Neradol D, 1 gm. = 10 c.c. N/10 NaOH, has been found to be the most suitable one for practical purposes. The author has, however, successfully employed some neradols of considerably higher acidities. The acidity above mentioned is possessed by a Neradol D containing 17 per cent. ash and 30 per cent. sodium sulphonates and Glauber's salts crystals respectively. This large quantity of salts present on the one hand effects the rapid pickle and tanning effect exhibited by Neradol D, on the other hand it also effects the softness in the leather resulting from its use either alone or in admixture with natural tannins.

4. Phlobaphene Solubilising Action of Neradols

A special feature of Neradol D is its property of solubilising phlobaphenes, which may be ascribed to its contents of sulphonic acids or their salts. In order to demonstrate whether the sulphonic acids and their salts are capable of solubilising the insoluble or sparingly soluble anhydrides of the tannins (the phlobaphenes) before and after condensation, the following experiments were carried out:—

Crude Argentine solid quebracho extract was converted into a highly viscous liquid by treating it for several hours with water at 100 C., and the anhydrides rendered insoluble by diluting the liquid with a large volume of cold water. The precipitate formed, consisting of quebracho phlobaphenes, was separated from the liquid by decantation, and purified by washing it several times with water. Each 10 gm. of this moist paste were treated in the cold with (a) free phenolsulphonic acid; (b) sodium phenolsulphonate; (c) crude Neradol and (d) Neradol D, 20 c.c. of water at 45 C. added, and the mixture allowed to cool slowly; the following solutions resulted:—

(a) Opalescent solution, much deposit, (b) Clear solution, no deposit. (c) Nearly clear solution, very little deposit. (d) Clear solution, no deposit.

This clearly proves that free and condensed phenolsulphonic acids as such are not capable of completely solubilising phlobaphenes, whereas the sodium salts of free and condensed phenolsulphonic acids possess this property. The salt contents of Neradol D, therefore, constitute an advantage in this respect, that not only may Neradol D be mixed with solutions of any natural tannin without insolubles being thereby deposited, but it may also be added in large quantities to a tannin solution with the result that the sparingly soluble and wholly insoluble constituents (phlobaphenes) are completely brought into solution.

The practical importance of the solubilising effect of Neradol D relating to solid Argentine quebracho extract is demonstrated in the following series of investigations carried out by the author:— [Footnote: Collegium, 1913, 478; Austr. Pat., 68, 796.]

Solid Neradol Matters Tanning Abs. Increase Argentine D. Calc. of Mixture Increase per Quebracho Found. in Tanning 100 gms. Extract. Matters. Extract.

Gm. Gm. Per Cent. Per Cent. 100 0 66.0 66.0 ... ... 0 100 32.5 32.5 ... ... 90 10 62.7 64.7 2.0 2.2 80 20 56.1 58.7 2.6 3.3 60 40 52.6 56.9 4.3 7.1 50 50 49.3 55.2 5.9 11.8 30 70 42.6 47.3 4.7 15.6 20 80 39.2 42.3 3.1 15.5

The maximum solubilising effect is exhibited in the mixture of 70 parts of Neradol and 30 parts of quebracho, with an additional percentage of tanning matters in the mixture of 15.6 per cent.—a figure which is very nearly identical with that of the insolubles present in the original Argentine quebracho extract.

The phlobaphene-solubilising property of Neradol D is closely connected with the influence of the latter on the colour of leathers tanned with natural tannins. If, on the one hand, a pelt is tanned with natural (i.e., non-treated) quebracho extract, a rather light coloured leather results, the fleshy colour of which is characteristic of quebracho. The dark coloured phlobaphenes present, on account of their insolubility, will have no influence on the colour of the leather. If, now, the quebracho extract be treated with sulphite and bisulphite in the usual way, the phlobaphenes are solubilised, but the reducing effect of the bisulphite tends to brighten the colour of the otherwise dark coloured phlobaphenes as well as that of the soluble tannins, and a reddish-yellow coloured extract results, imparting its own colour to the pelt. When, on the other hand, the quebracho extract is solubilised by means of Neradol D, the phlobaphenes are brought into solution without reduction taking place, and a dark brownish-red extract results, which imparts a similar colour to the finished leather. This darkening effect of Neradol D is most conspicuous in the case of mangrove, maletto, and chestnut, but is absent in the case of algarobilla, dividivi, gambir, sumac, and valonea. The varying phlobaphene contents of the tannins easily afford an explanation of the different properties above alluded to: the mangrove phlobaphenes are dark coloured bodies, those of mimosa, maletto, and chestnut are of lighter colour, and the last-named tanning materials enumerated above are either devoid of phlobaphenes or possess them only as very light coloured bodies. Algarobilla, sumac, gambir, dividivi, and valonea, on the other hand, are associated with large amounts of sparingly soluble ellagic acid, known as "bloom" or "mud" which imparts a light colour to the finished leather, and conveniently covers the dark colour imparted to the leather by other tanning materials; for this reason the former are often used in the lay-aways or in the finishing processes.

Similar effects to those of Neradol D are exhibited by other salts of sulphonic acids, e.g., sodium benzylsulphanilate (Solvenol B.A.S.F., or solution salt ("Solutionsalz") Hoechst); the author prepared mixtures of such salts and untreated quebracho extract in order to determine their solubilising effects, and arrived at the following results:—

30 parts Solvenol plus 70 parts quebracho extract: clear solution, no deposit.

25 parts Solvenol plus 25 parts quebracho extract: clear solution, very little deposit

20 parts Solvenol plus 80 parts quebracho extract: nearly clear solution, very little deposit.

15 parts Solvenol plus 85 parts quebracho extract: slightly opaque solution some deposit.

Leathers tanned with these mixtures were more or less dark coloured according to the amounts used of solvenol and the consequent solubilisation of the phlobaphenes.

A similar effect, though of opposite nature from a tanning standpoint, is exhibited by sulphonates on certain colloidal dark coloured substances. A phenolsulphonic acid, which had been overheated during sulphonation and subsequently condensed (crude Neradol), imparted a conspicuous greyish-brown colour to the leather; samples of this crude product were then partly neutralised with varying amounts of alkali, and these samples (containing increasing quantities of salts) tested for tannin and colour effects. It was found that the more highly neutralised samples imparted a darker colour to the solutions, but these dark products did not deposit the dark impurities on the pelt. One may therefore assume that tannoid substances are colloidally suspended, and when converted into true solutions are incapable of being fixed in insoluble form by the pelt.

Just as, by adding Neradol D to a tanning extract, the phlobaphenes are solubilised and a dark coloured extract results, it is also possible to remove the mechanically deposited phlobaphenes and oxidised tannins from the finished leather, and, as a consequence, lighten the colour of the leather. For practical purposes, bleaching with Neradol D is carried out by brushing over the darkly coloured leather with a 2-3 B. solution of Neradol D, and then rinsing well with water, in order to remove the solubilised tannin. A lighter colour may also be obtained by immersing the leather in a liquor of the strength mentioned above for several hours, and then rinsing with water, but by this procedure not only the surface tannin is removed, but also tannin from the leather substance itself; this method is therefore not suitable for heavy leathers which are sold by weight.

The advantage of employing Neradol D as a bleach in this way is to be found in the fact that, on the one hand, the bleaching sulphonic acid attacks the leather to a much slighter extent than is the case with inorganic acids usually employed for this purpose; on the other hand, the method of brushing the sulphonic acid on the leather only introduces small amounts of sulphonic acid in the leather, thus lessening the harmful effects of acids upon leather. Furthermore, the common methods of using alkalies as tannin-solubilising agents with the consequent running off and waste of alkaline tan liquors are here substituted by a method leaving liquors rich in tannin and Neradol, and which may be used in the ordinary procedure of tannage.

Since Neradol D contains neutral sodium sulphate (about 3 per cent.), and the latter, by precipitating colouring matters present in tan liquors, may slightly bleach these, it was of interest to determine whether the sodium sulphate plays any part in the bleaching effected by Neradol. Mixtures of chestnut and quebracho extracts were prepared, to which were added:—

(1) 5 per cent. Neradol D. (2) 5 per cent. Neradol D. free from Na2SO4. (3) 15 Per cent. sodium sulphate (corresponding to above Neradol D).

These mixtures were allowed to act upon pelt alongside of comparison tests using quebracho and chestnut extracts only, the strength of the liquors in all cases being 1.5 B; the pelt was left in the solution till tanned through. The following results were obtained:—

(1) Quebracho tanned leather was darker; no difference in colour by chestnut extract. (2) Similar to (I). (3) Same colour as given by the original extracts.

This experiment demonstrates that absence of sodium sulphate in the mixture is without influence on the colour of the resulting leather, and that an addition of sodium sulphate to natural extracts does not affect the colour imparted by them to pelt

5. Effect of Neradol D on Pelt

Being a sulphonic acid derivative, the chemical constitution of Neradol is obviously considerably different from that of the natural tannins, and the question has been asked: Will Neradol D, in its concentrated form, attack the hide substance?[Footnote 1: Collegium, 1913, 521, 487.] Bearing in mind that concentrated extracts of vegetable tannins in some circumstances effect a "dead" tannage (cf. case-hardening) and hence reduce their practical value, and that for this reason it is impossible to allow either concentrated extracts or concentrated Neradol D to act upon pelt, the author still decided to carry out some experiments in this direction. Concentrated Neradol D (33 B.) and strong aqueous solutions of this material in strengths of—

30 25 20 15 10 5 3 1 B.

were therefore allowed to remain in contact with pelt for a period of ten days, when the pelts were taken out and washed in running water for twenty-four hours, and then dried. The resultant leathers possessed the following properties:—

33 B. solution: completely gelatinised.[Footnote 2] 30 " " " [Footnote 2] 25 " two-thirds gelatinised; surface tanned. 20 " one third gelatinised; surface "dead" tanned. 15 " pelt was glassy throughout. 10 " rather cracky leather, but well tanned. 5 " normal tannage. 3 " " " 1 " " " [Footnote 2: Impossible to subject the pieces to a proper washing out.]

The interiors of the leathers obtained from the 25 and 20 B. solutions were completely gelatinised; this may be accounted for by assuming that the surface was "dead" tanned, and that hence the free dissociated sulphonic acid diffused into the leather, towards which it exhibited hydrolysing rather than a tannoid effect with the consequent result described above. Above 10 B. the effect is more that of an acid with concentrations below 10 B.—the only ones of technical importance—however, no ill-effects may be observed.

For tanning purposes, Neradol D solutions of 2 B. are quite satisfactory, and it has been found [Footnote 1: Technikum, 1913, 80, 324.] that solutions of this strength do not dissolve out any protein of the hide. [Footnote 2: The translator cannot agree with the author on this point. He has, for instance, found that solutions of analytical strength dissolve considerable amounts of hide substance, and his practical experience confirms results arrived at in the laboratory.]

A purely Neradol D tanned leather may be produced by immersing a bated pelt, free from lime, in a 2 B. Neradol D liquor for about four days; the resultant leather being nearly white and otherwise very similar to a leather tanned with vegetable tanning materials.

The main application of Neradol D is in admixture with vegetable tanning materials; especially in the early stages of tannage is this substance of value, since by its use not only a light coloured leather surface is obtained, but its presence prevents a subsequent dead tannage when strong vegetable tan liquors are applied, and it also imparts strength to the grain layer. It is thus possible to shorten the time consumed by the tanning process by employing Neradol D in the manner described.

A further explanation as to why the tanning process is considerably hastened by using Neradol D, either alone or in conjunction with natural tannins, is afforded by the fact that though Neradol D quickly penetrates the grain, it is but "loosely" fixed by the latter, i.e., it is not deposited to such an extent that it would prevent penetration of the vegetable tannins. In the case of a mixture of Neradol D and vegetable tannins, the former quickly diffuses into the pelt and fixes the fibres, thus facilitating penetration of the vegetable tannins. This assumption is justified in view of the speed with which Neradol D completely penetrates and tans the pelt, since Neradol D containing acids and salts exhibits effects similar to those of a pickle.

6. Reactions of Neradol D with Iron and Alkalies

A special characteristic of Neradol D tannage is the sensitiveness of the latter to the action of iron and alkalies. The active principle of Neradol D being free dicresylmethanedisul-phonic acid, which is easily neutralised by lime, ammonia, and amino-acids and hence rendered inactive for tanning purposes, it is essential that the pelt prior to tannage with Neradol D should be completely delimed, bated, and freed from all constituents possessing alkaline reaction. It is, however, possible to regenerate Neradol D liquors contaminated with alkali or partly neutralised by the addition of small quantities of organic (formic, acetic, lactic, and butyric) or inorganic (hydrochloric or sulphuric) acids,i.e., the dicresyl-methanedisulphonic acid is again partly liberated, and this procedure is always preferred where the tanning process does not allow of a complete deliming of the pelt prior to introducing the latter into a Neradol D liquor. If, on the other hand, such liquors are kept properly, and the addition of acid referred to kept up, they will remain active for weeks and need only strengthening up with the requisite quantity of Neradol prior to introducing fresh pack.

The sensitiveness to alkalies of Neradol D is considerably greater than in the case of natural tannins, and it appears that a vegetable tan liquor neutralised with lime will not even surface-tan when acting upon pelt and will neither impart a dark colour to the leather nor remove from it any appreciable amount of protein. Similarly, a Neradol D liquor neutralised with lime exerts no tanning action, but in contradistinction to the vegetable tan liquor similarly treated, will impart a blue or blackish-blue colour to the pelt, from which it removes larger quantities of protein. The author examined two such liquors relating to their contents of tanning matters and protein and obtained the following results:—

Reaction. Bark. Tans. Non-Tans Insol. Proteins

Per Per Per Per Cent. Cent. Cent. Cent.

Vegetable Slightly 12 0 2.93 0.35 0.01 tan alkaline liquor

Neradol " " 10 0 4.43 0.17 0.17

These figures do not only show the higher protein contents of the Neradol D liquor, but do also show higher contents in soluble non-tannins, which consist mainly of lime (2.12 per cent.) and sodium salts (1.8 per cent.), thus establishing the fact of the sensitiveness of Neradol D to alkalies in addition to its lime-solubilising effects.

The sensitiveness towards alkalies is also noticeable on a large scale where the tanpits have been built of cement; though the pelt may be quite free from lime, the Neradol D is quickly neutralised by the cement, with results similar to those enumerated above.

The blue coloured soluble compound of Neradol D and iron salts, to which frequent reference has been made, is very important from a practical standpoint. Whereas the catechol tannins (i.e., fir, gambir, hemlock, cutch, mangrove, and quebracho) are coloured black, those of the pyrogallol class (i.e., algarobilla, dividivi, valonea, gallotannic acid, myrabolams, and sumac) bluish-black, and the "mixed" tannins (i.e., canaigre, oak, and mimosa bark) bluish-purple by iron alum, Neradol D is coloured a pure blue. How sensitive this reaction is, the following comparative analyses illustrate: to each litre of tan liquor containing 4 gm. tanning matter prepared from (a) quebracho extract and (b) Neradol D, 10 c.c. of a 10 per cent. iron alum solution were added, the solutions heated to 100 C., cooled and filtered, and the colour of the filtrates and the weight of the precipitates determined:—

(a) Quebracho solution: light reddish-brown filtrate, 3.22 gm. precipitate.

(b) Neradol solution: deep blue filtrate, 0.02 gm. precipitate.

Hence, on adding a soluble iron salt to a solution of a natural tannin, most of the tanning matter is precipitated; the colour of the filtrate, however, is much the same as that of the original solution. A Neradol D liquor similarly treated gives no precipitate, but is coloured blue throughout. The filtrates from the above solutions were allowed to act upon pelt, and the following observations were made:—

(a) The light reddish-brown filtrate from the quebracho liquor exhibited no well-defined tanning effect on pelt, to which it imparted a light brown colour.

(b) On the other hand, the deep blue filtrate from the Neradol D liquor exhibited well-defined tanning effects, and imparted a deep blue colour to the pelt.

For practical purposes, the sensitiveness of Neradol D to iron is not only remarkable because any contact with iron particles will colour the liquor (and hence the pelt) blue, but also because the slight amount of iron always present in cement renders the use of cement pits prohibitive where Neradol D liquors are used.

This intense blue coloration might have made possible a colorimetric estimation of Neradol D. The author has investigated this possibility, using different concentrations of Neradol D liquors to which a solution of iron ammonium alum was added, and found that when, at certain concentrations, the maximum blue colour had been obtained, it was still possible to increase the quantity of Neradol without the intensity of the colour being affected. Addition of a little alkali tends at first to darken the blue colour, more alkali changes the blue colour to brown and yellow, successive additions of a weak organic acid (e.g., acetic acid) rapidly lighten the blue colour. Since industrially used Neradol D liquors always contain varying quantities of acid and may be neutral or even slightly alkaline, it must be considered impossible to make any use of such a colorimetric estimation for practical purposes.

7. Reagents Suitable for Demonstrating the Various Stages of Neradol D Tannage

The extent to which tannage with Neradol D proceeds on the surface and within the pelt may be judged from the feel of the skin, but such a method is totally unsuited to any but a practical tanner. A suitable and reliable reagent is indigotine (B.A.S.F.), which clearly distinguishes tanned and untanned layers of the pelt. If, for instance, a 1-2 per cent, solution of indigotine is brought into contact with a fresh cut on a pelt, and the latter subsequently washed with warm water, the indigotine is only retained by the untanned parts; a leather tanned with Neradol D is therefore only coloured by indigotine to the extent to which it has combined with the Neradol. [Footnote: According to Seel and Sander (Zeits. f. ang. Chem., 1916, 333), basic dyestuffs are also very suitable for demonstrating tanned parts of the pelt.]

Another reagent is constituted by iron ammonium sulphate; the extent of the penetration of Neradol D, which gives an intense blue coloration with iron salts, into the leather may be determined by washing the pelt treated with Neradol D, making a cut, again washing and treating the cut with a few drops of a weak solution of iron ammonium sulphate. Those parts of the pelt which have been converted into leather then appear deep blue; on the other hand, those which have been in contact with Neradol D, but have not yet been converted into leather, are light blue. Those parts which have not yet been in contact with Neradol D appear pure white; the results of this reaction are therefore opposite to those obtained by the use of indigotine.

8. Combination Tannages with Neradol D

Whereas mixtures of Neradol D and vegetable tannins impart properties to the leather consistent with the proportions in which these materials are present, it is not possible to combine Neradol D with mineral tanning agents or fats (e.g., fish oils, etc.) in such a way that a leather characterised by the properties of either material is obtained. Experiments were carried out using (1) chrome salts plus Neradol D; (2) aluminium salts plus Neradol D; and (3) oils plus Neradol D, and the following conclusions were arrived at:—

1. CHROME-NERADOL D liquors, containing comparatively larger amounts of Neradol D, act too rapidly on the pelt and draw the grain; smaller amounts of Neradol D seem without influence on the finished leather, which possesses pronounced characteristics of chrome leather. Another disagreeable factor is the following: the chrome salts must possess a certain degree of basicity in order to produce good leather; the Neradol D must, on the other hand, possess a certain acidity to produce the optimum results, and it is hence impossible to balance practically the basicity of the chrome salts and the acidity of the Neradol in order to justify the presence of both. If one of the two is used separately before the other, a leather always results possessing the characteristics of the material first employed, provided the time of action has been sufficiently extended. If insufficient time has been allowed, the characteristics imparted by the main tanning agent are not altered.

2. ALUMINIUM SALTS AND NERADOL require practically the same basicity and acidity respectively, and when combined always yield a leather possessing mainly the properties of one of the components. In addition to this fact, leathers tanned with aluminium salts possess great softness and stretch, those tanned with Neradol D greater firmness and less stretch, and these opposing qualities completely compensate one another and render nil the value of such mixtures.

In addition to this, the presence of aluminium salts produces no better fixation on the leather fibre of basic coal-tar dyes, so that in this respect also a combination of aluminium salts and Neradol D is of no value.

3. FAT NERADOL D TANNAGE: Just as aluminium salts impart special characteristics to leather, this property is exhibited by fatty matters, especially so as regards stretchiness and softness. Both of the latter are not apparent to the same extent in an oil tannage into which Neradol D and oil enter as constituents. It is, however, not excluded that, in view of the fact that the combination of oils and Neradol D appear to produce the most promising results of the three from a technical point of view, such combination would yield products possessing less stretch and greater softness which, by occupying an intermediary position, might possess certain advantages and be useful for certain technical purposes.

9. Analysis of Leather Containing Neradol D

Chemical examination of leathers tanned with Neradol D or with mixtures of natural tannins and Neradol D often involve a determination of the materials employed in tannage. In most leathers exclusively tanned with vegetable tanning materials, it is usually possible to determine at least the nature of the main tanning agent, whereas the attempts at determining those tannins which are only present in minor quantities rarely succeed. Since Neradol D usually is employed in comparatively small quantities, it has been imperative to find a method which also permits of the detection of smaller quantities of Neradol D. Provided the presence of not less than 5 per cent. (on the weight of the leather) of Neradol D, the following method yields reliable results:—20-30 gm. of the leather are ground or sliced as finely as possible and the powder (or the slices) treated in the cold with a sufficient volume of dilute ammonia solution (5 c.c. ammonia plus 95 c.c. of water) for eight to twelve hours. The object of this is to dissolve the tannins, but no protein should go into solution. The solution is filtered and the filtrate evaporated on the water bath till it occupies a volume of about 30 c.c. A few c.c. of aniline hydrochloride are now cautiously added, when it should be carefully noted if a precipitate is thrown down which might be either completely or only partly soluble in excess of aniline hydrochloride. A precipitate is always thrown down when Neradol D or wood pulp is present; only the Neradol D precipitate is soluble in excess of aniline hydrochloride. Partial solubility of the precipitate therefore indicates the presence of both wood pulp and Neradol D.

The quantitative determination of sulphuric acid—the detection and estimation of which in leather is important—is considerably influenced by the presence of Neradol D. Practically all methods in vogue dealing with its determination were based on the estimation of the sulphur introduced into leather by sulphuric acid. The presence of Neradol D, the main constituent of which is dicresylmethanedisulphonic acid, renders it impossible by such methods to determine whether the combined sulphur owes its origin to sulphuric or sulphonic acid. It remains yet to be determined whether the sulphonic acid influences the leather substance to the extent that sulphuric acid does; it must, however, be borne in mind that Neradol D in addition to free sulphonic acid also contains sulphonates and sulphates, which may enter into the leather and thus increase the sulphur contents of the latter. A method must hence be devised which estimates the free acid only and provides the means of distinguishing this from all other acids of organic and inorganic acids. Paessler, [Footnote: Collegium, 1914, 527, 126; 531, 509; 532, 567.] by extracting the leather and dialysing the filtrate, has effected a separation of the acids and the tanning and colouring matters and quantitatively estimated the sulphuric acid in the dialysate.

Immerheiser [Footnote 1:Collegium, 1918, 582, 293.] devised a method, based upon the property of sulphuric acid of combining with ether, for the purpose of determining free sulphuric acid in leathers:—10 gm. of the leather, cut into small pieces, are extracted three times with 200 c.c. distilled water at room temperature, the time of each extraction being ten to twelve hours, and the combined extracts evaporated to dryness on the water bath, 5 gm. of quart sand being added. The dry residue is now powdered, introduced into an Erlenmeyer flask provided with a glass stopper, and 200 c.c. of anhydrous ether [Footnote 2: To be tested for water by shaking with anhydrous copper sulphate.] added. After about two hours, during which the flask is occasionally shaken, the ether is poured through a filter, the residue washed with a little ether, and the operation repeated twice with each 40 c.c. anhydrous ether, using the same filter. To the combined ether extracts (about 200 c.c.) HCl and [Greek: b]aCl2 are added, the ether distilled off and the residue evaporated on the water bath, in order to decompose the ether-sulphuric acid compound. 50 c.c, of hot water acidified with HCl are now added, the precipitate allowed to settle, filtered, washed, dried, and weighed. The sulphuric acid thus estimated was present in the leather as free sulphuric acid. That present as sulphates soluble in water is estimated in the residue on the filter: the residue is extracted with hot water, the sand filtered off, the filtrate acidified with HCl, boiled for one quarter hour and filtered if necessary. The clear filtrate, which may be coloured, is brought to boil and [Greek: b]aCl2 is added. The barium sulphate indicates the sulphuric acid present in the leather as water-soluble sulphates.

Whether the latter be sulphates or bisulphates may be indicated by the aqueous extract of the above residue, since neutral reaction would indicate the absence of bisulphates, acid reaction their presence in addition to possible normal sulphates; the quantitative estimation of the metals would decide this point definitely.

10. Properties of Leathers Tanned with Neradol D

Whereas the colour of leathers tanned with Neradol D only is nearly a pure white, those tanned with mixtures of Neradol D and vegetable tanning materials are more or less light coloured according to the quantity of Neradol D present, as has been explained when discussing the phlobaphene-solubilising action of Neradol D. In any case, all leathers tanned with Neradol D possess fibre of remarkable length, which explains their increased tensile strength and elasticity. The tensile strength of a leather tanned with a mixture of Neradol D and vegetable tannins was 3.7 per cent, as compared to 3 per cent when no Neradol was used; the extension was 56 per cent, when tanning with Neradol D as against 36 per cent, without the latter.

The sensitiveness to light of leathers tanned with Neradol D may be mentioned. Exposed to direct sunlight, the surface of the leather assumes a yellowish colour after two days' exposure, and assumes a pure yellow colour after a further three days. A further fifteen days' exposure only darkens the leather slightly, the final colour being very little different from the one obtaining after five days' exposure.

In passing, it may be remarked that this yellow colour is observed on the surface only, the grain otherwise possessing that pure white colour characteristic of Neradol D tanned leather. Further, it may be noted that leathers tanned—with Neradol D fix basic coal-tar dyes excellently, whereas acid and substantive dyestuffs are fixed with other than their natural shades.

The author has analysed a leather exclusively tanned with Neradol D, and has obtained the following results:—[Footnote: Collegium, 1913, 521, 478.]

Moisture - - - - - 15.53 per cent. Ash - - - - - - 0.93 per cent. Fats- - - - - - 1.26 per cent. Extraneous matters - - - 0.00 per cent. Leather Substance Tanning matters- 36.92 per cent. Leather Substance Hide substance - 45.36 per cent. - 100.00 per cent. [Footnote: Sp. gr., 0.642.]

From these figures, those of "degree of tannage" and "yield" (pelt—>leather) are calculated as 81.4 and 220 respectively.

These figures correspond closely to those obtained by the analysis of leathers tanned with vegetable tanning materials, and this proves the similarity between the Neradol D tannage and a vegetable tannage in their chemical aspects.

11. Neradol D Free From Sulphuric Acid

In order to prepare phenol and cresulphonic acids, such quantities of technical sulphuric acid are used as do not allow of the assumption of complete utilisation of the sulphuric acid; hence it was of theoretical interest to remove eventual traces of free sulphuric acid from the product. For this purpose, the author diluted crude Neradol to 20 B. and gradually added small quantities of milk of lime; the precipitates were freed from the liquid by suction and washing, and a Neradol free from sulphuric acid resulted, which was then brought to the acidity of Neradol D with the calculated amount of alkali. From the calcium sulphate precipitate, the amount of sulphuric acid originally present was calculated, and was found to be only 4 per cent.

The acid-free sample of Neradol was tested with regard to its suitability as a tanning agent; leather tanned with this sample differed from one tanned with an untreated sample (Neradol D) by being harder and possessing a pronouncedly greyish colour. This difference, however, may not be due to the absence of sulphuric acid but to the presence of the slightly soluble calcium sulphate in the sample treated with milk of lime. To prove this point, another way of preparing Neradol D free from sulphuric acid was looked out for. Sodium acetate was added to a solution of crude Neradol until the latter was no longer acid to congo-red; at this point no free sulphuric acid can be present in the solution. The product, partly neutralised till the acidity of Neradol D was reached (part of the acidity then being due to liberated acetic acid), yielded a leather which neither in colour nor in feel differed from the usual Neradol D tanned leather. This proves that the grey colour and the hardness of the leather described in the former experiment is due to the presence of calcium sulphate.

If the crude Neradol treated with sodium acetate is not partly neutralised, the analysis gives the following figures:—

Tanning matters 67.3 per cent. Soluble non-tannins 8.6 " Insolubles 0.0 " Water 24.1 " ————- 100.0 per cent. Acidity: 1 gm. = 46 c.c. N/10 NaOH.

Compared to the analysis of crude Neradol containing sulphuric acid, the figures show that, on the one hand, the presence of the comparatively small quantity of sodium acetate but slightly influences the contents of non-tannins and water, but, on the other hand, reduces the contents of tannins and also the acidity. The tanning intensity of this product, however, is considerably increased, and using a 1 B. solution a leather is obtained in a very short time very similar to that yielded by ordinary Neradol D, but considerably harder; the latter property is due to higher acidity and almost complete absence of salts in the product treated with sodium acetate.

The author finally attempted to partly neutralise crude Neradol with various hydroxides and carried out tanning tests with samples containing the different metals. Hardly any difference in the finished leathers could be observed as regards colour or quality; the tannage could by no means be described as that of a combination of Neradol D and the respective metals.

12. Neutral Neradol

Crude Neradol, completely neutralised with caustic soda, yields a product of the following composition:—

Tanning matters 19.8 per cent. Soluble non-tannins 37.9 " Insolubles 0.0 " Water 42.3 " —————— 100.0 per cent.

The qualitative reactions of this product differ from those of non-neutralised Neradol to the extent that gelatine is not precipitated and iron salts are not coloured blue, but dirty brown, by the aqueous solution of this product.

The completely neutralised product, diluted to various concentrations (of 1, 2, 3, and 5 B.) and tested as to tanning properties, revealed the surprising fact that the pelts were not even surface tanned, and were coloured evenly blue throughout by indigotine.

It might have been anticipated that sodium dicresylmethanedisulphonate would be as devoid of tanning powers as is a neutralised vegetable tannin, but it is difficult to explain the fact of the sodium salt being adsorbed by hide powder as "tanning matters" in the Official Method of Analysis. Brought to a logical conclusion, the figure 19.8 per cent, should be deducted from 32.5 per cent, obtained in the analysis of a partly neutralised Neradol D, which comparatively large quantities of the sodium sulphonate also adsorbed by hide powder, leaving the "tanning matters" of Neradol D at 13.5 per cent.

This diminished figure, however, does in no way reduce the value as a tanning agent of Neradol D; it merely shows how inadequate is the hide powder method of analysis when applied to substances of the composition of Neradol D. This is further confirmed by the Loewenthal permanganate method, which yields the following figures:—

Tanning matters 7.2 per cent. Soluble non-tannins 59.1 [Footnote: Collegium, 1913, 521,487.]

If, on the other hand, completely neutralised Neradol is acidified with an organic acid, such as acetic acid, till the acidity, (1 gm.= 10 c.c. N/10 NaOH) is reached, the resulting product is in all respects similar to Neradol D and yields a corresponding leather.

It is permissible to assume that the irregularity exhibited by Neradol D as regards the analytical estimation of its tannin contents is connected with the low molecular weight of the tanning principle. Whereas all tannins so far isolated from the natural tanning materials possess rather high molecular weights, that of Neradol D deviates considerably from this rule, as is shown by the following table:—

Neradol D tannin Cl5H16S2O8 358 Mangrove " C24H40O2l 670 Oak bark " C28H28O23 840 Myrabolam " C54H48O35 1256 Dividivi " C54H46O35 1270 Malletto " (C4lH50O20)2 1724

This low molecular weight may mainly account for the figures obtained by the incorrect oxymetric estimation with permanganate; the apparent tannoid property of the tannoid-inactive neutral salt of dicresylmethanedisulphonic acid may be explained by assuming that though it is, probably, in the colloidal state, and as such adsorbed by hide powder, it is still devoid of astringent properties.

G. Different Methods of Condensation as Applied to Phenolsulphonic Acid

In addition to formaldehyde, many other substances may, theoretically, induce condensation of phenolsulphonic acid; condensation takes place either with the elimination of water or, in addition to this, with the introduction of methane group.

So far, the following condensing agents have been investigated:—

(1) Heating in vacuo. (2) Sulphur chloride. (3) Phosphorus compounds. (4) Aldehydes. (5) Glycerol.

1. Condensation Induced by Heat

If phenolsulphonic acid is heated in vacuo at 130 C. for twenty hours, condensation takes place [Footnote: Austr. Pat., 64,479.] without the addition of any condensing agent, and an anhydride of the

^ O ^ v v HSO3 HSO3

composition is formed. This product is a viscous liquid, possessing a very corrosive action. Added to a solution of gelatine, a light, fine flocculent precipitate is thrown down. Analysed by the shake method of analysis, the tannin content of the product equals about 46 per cent. Its strongly acidic and hence swelling character does not express qualities consistent with the conception of suitability for tanning purposes: a sample of the product was therefore partly neutralised to the acidity of Neradol D, when the shake method of analysis yielded the following figures:—

Tanning matters 21.5 per cent. Soluble non-tannins 48.3 " Water 30.2 " ——————— 100.0 per cent.

This partly neutralised sulphonic acid represents a white, pasty mass, which is not particularly easily soluble in water, yielding a solution of milky appearance. Treated with the usual tannin reagents, it exhibits the following characteristics:—

Gelatine Light Flocculent precipitate. Bromine water Compete fixation. Ferric chloride Cherry-red coloration. Lead acetate Very slight Percipitate, insoluble HNO_3. Aniline hydrochlonde Slight percipitate.

Solutions of this product in concentrations from 1-8 B. exerted no tanning action whatever, whereas more concentrated solutions (15 B.) converted pelt in eight days into a leather very similar to a Neradol D leather in colour and feel, but considerably harder.

In order to determine its phlobaphene-solubilising effects, samplesof the product were mixed with concentrated quebracho extract in the proportions 5,10, 20, and 30 per cent. on the weight of extract, and the following observations made:—5 and 10 per cent. were without effect, 20 and 30 per cent. showed some solubilising tendency, but on diluting the mixture with water the quebracho was completely thrown out of solution. Apparently this anhydride is, in this respect also, quite different from the partly neutralised diphenylmethanedisulphonic acid.

2. Condensation with Sulphur Chloride

When sulphur chloride is allowed to act upon phenolsulphonic acid whilst heat is applied, a yellowish-grey mass results, which dissolves in water, forming a reddish-yellow solution. Neutralised to acidity 10, it exhibits the following reactions:—

Gelatine————————Precipitate. Ferric chloride————-Deep blue coloration. Lead acetate——————White precipitate, insoluble HNO_3. Aniline hydrochloride—-Precipitate. Bromine water—————-No reaction.

The partly neutralised 2 B. solution of this product yielded a reddish-grey coloured leather, the qualities of which were very similar to that yielded by Neradol D.

3. Condensation with Phosphorus Compounds

Schiff's well-known synthesis, [Footnote: Liebig's Ann., 178, 173.] in which phosphorus oxychloride interacts with phenolsulphonic acid, yields a product which exhibits some tannin reactions, but which, when acting on pelt, converts the latter into a leather which, when dried, is very cracky. If, on the other hand, cresolsulphonic acid is condensed with phosphorus oxychloride by heating the two together, products eminently suitable for tanning purposes result. These products are non-crystalline bodies easily soluble in water, and are coloured bluish-violet by ferric chloride and precipitate gelatine. Solutions of the free acids and acidified solutions of the salts convert pelt into firm and white leathers possessing great softness and pliability.[Footnote: Austr. Pat, 66,895.]

4. Condensation with Aldehydes

By treating phenolsulphonic acid with acetaldehyde in the usual way, a viscous brown mass is obtained, which is very soluble in water, the solution being of a brown colour. When brought to acidity 10, the following reactions are exhibited by the product:—

Gelatine - - - Precipitate. Ferric chloride - - Deep blue coloration. Aqueous ammonia - - Cherry-red coloration. Lead acetate - - - Yellowish precipitate, insoluble HNO_3. Aniline hydrochloride - - Yellow precipitate, soluble excess aniline. Bromine water- - - No reaction.

Tanning experiments with this substance yielded, even after extended tannage, an undertanned leather, the surfaces being coloured brown, the inner layers, however, white. Further neutralisation reduces the tanning intensity of the product; the addition of sodium sulphate to the original partly neutralised product hastened tannage, the leather, however, possessing dark colour and being undertanned. The following constitution may be ascribed to this product:—

OH OH ^ -CH2 -CH2 - ^ v v HSO3 HSO3

If benzaldehyde is used in lieu of acetaldehyde for condensing phenolsulphonic acid, a water-soluble product results, exhibiting reactions similar to those of the acetaldehyde-condensation product. The former product is more suitable as a tanning agent and yields a reddish-brown rather firm and hard leather; it possesses the constitution—

H OH OH ^ C ^ ^ v v HSO3 v HSO3

For the purpose of condensing phenol with formaldehyde, it is not essential to first convert the phenol into the water-soluble phenolsulphonic acid, since it is possible to convert the condensation products of phenol and its derivatives, which are soluble in alkali, into water-soluble form by either heating the condensation products with concentrated solutions of formaldehyde and neutral sulphites, or by dissolving the condensation products in alkali and inducing reaction by means of formaldehyde bisulphite. [Footnote: Collegium, 1913, 518, 324.] Highly concentrated solutions result, which may be concentrated either as such or after the alkali present has been neutralised. The sulphurous acid formed prevents oxidation of the product on evaporation. A special advantage of this method of preparation is the fact that sulphuric acid, which is but difficultly removed from the end-product, is not employed at all.

The product thus obtained is a yellowish-white crumbly mass, which is very soluble in water, forming a clear solution. The latter exhibits the following reactions:—

Gelatine———————-Precipitate. Ferric chloride————Deep blue coloration. Aqueous ammonia————Cherry-red coloration. Lead acetate—————-White precipitate, insoluble in HNO_3. Aniline hydrochloride—Precipitate. Bromine water—————No reaction.

The product brought to acidity 10, yielded on analysis the following figures:—

Tanning matters————————— 25.2 per cent. Soluble non-tannins——————— 56.3 " Insolubles———————————- 0.0 " Water—————————————— 18.3 " ——————- 100.0 per cent.

Tanning experiments with this substance yielded white and soft leathers, which were indistinguishable from those tanned with Neradol D.

A characteristic feature of this synthetic tannin is its behaviour in concentrated form towards pelt, which is not attacked by it, but is readily tanned even at such high concentrations. An explanation of this is to be found in the large quantity of salts present in the product. A disadvantage of this synthetic tannin is its complete incapability of dissolving phlobaphenes, which is even so far extended as to precipitate otherwise easily soluble tannins when adding it to solutions of the latter in comparatively large proportions; here, again, the salts are responsible for this behaviour, their large quantities effecting a salting out of the natural tannins.

The class of aldehyde condensations also comprises that of inducing condensation by means of sugars; if phenolsulphonic acid is heated with glucose, a reddish-brown liquid results, which is soluble in water. The solution exhibits reactions similar to those of Neradol D. It is, however, not possible, by this method of condensation, to prepare as highly concentrated products as is possible in the case of Neradol D, since employing sugars as condensation agents means liberation of a large volume of water. Analysis of this product, using the shake method, gives a tannin content of 16.2 per cent; tanning experiments demonstrated that the time of tannage, using a 2 B. solution, was the same as that required by Neradol D, and yielded a leather, the surface of which was reddish-grey, the inner layers being white, but which is otherwise very similar to Neradol D tanned leather. [Footnote: Austr. Pat, 69,375, 69,376, 69,377.]

Relatively to its capability of solubilising phlobaphenes, this product exhibits similar properties to that obtained by merely heating phenolsulphonic acid, to a slight extent only solubilising quebracho extract, which, on diluting the mixture, is completely thrown out of solution.

5. Condensation with Glycerol

Phenolsulphonic acid, when heated with glycerol, undergoes the process of condensation, and forms a brown fluid, which, when brought to acidity 10, exhibits the following reactions:—

Gelatine————————-Precipitate. Ferric chloride—————Brown-black coloration. Lead acetate——————-White precipitate, insoluble in HNO_3. Aniline hydrochloride——Slight precipitate.

Tanning experiments with this partly neutralised product resulted in a very gradual conversion of the pelt into a greenish-grey coloured leather; the colour, however, does not penetrate the pelt and is hence caused by colloidally suspended impurities. If the solution is filtered through a filter candle, a somewhat clearer solution results, but the latter also tans very slowly and yields a brown coloured leather.

Analysis of the partly neutralised product reveals a tannin content of 17.6 per cent. A 2 B. solution of the non-neutralised product showed a rapid tanning effect at first, when brought into contact with pelt, on which it had a strong swelling effect, and to which it imparted a greenish colour; the tanning effect, however, slowed down considerably, after a few days, and the solution penetrated the pelt only very gradually; this is probably due to the presence of large quantities of colloidally suspended impurities, which, when the substance is partly neutralised with the formation of salts of the sulphonic acids, are brought into true solution and hence penetrate the pelt with greater rapidity.



INDEX OF AUTHORS

Adler Appelius Ashmore

Bader Badische Anilin u.(German abbreviation for "und") Soda-Fabrik Baekeland Baeyer Berzelius Biginelli Boehringer & Sons Bottinger Braconnot Buff

Caro Chem. Fabrik Jucker & Co. Chevreul

Dekker Deutsch-Koloniale Gerb u. Farbstoff Gesellschaft Deyeux Diz Drabble

Edner Elberfelder Farbenfabriken

Fahrion Feist Fischer, E. Freudenberg Froda

Gerhardt Gesellschaft f.(German abbreviation for "fr") Chem. Industrie, Basle Graebe Graham Grasser

Hatchett Heinemann Herzig Herzog Hnig

Iljin Immerheiser

Jennings

Kahl Kauschke Klepl Knig Kostanecki Krafft Krauss Kunzemller

Lauffmann Liebig Lipp Lloyd Lwe

Manning Mauthner Meunier Michael Mielke Mitscherlich

Nierenstein

Paessler Patern Payne Pelouze Perkin Proust

Rapoport Raschig Reinsch Resch Russanow

Sabanajew Sander Scheele Schiff Schmidt Schorlemmer Seel Seyewetz Sisley Skey Stiasny Strauss

Thuau Tschirch

Vogel

Walden Webster Weinschenk Wohl

Zacharias



A

Alcohol figure Algarobilla Alizarin Alizarin yellow, in paste Alkalies, reaction of, to Neradol D Alum-neradol tannage Alum tannage Aminobenzene Aminophenol, p- Aniline dyes Anthracene Anthraquinone Arylsulphaminoarylsulphonic acids Arylsulphoxyarylsulpho acids

B

Bakelite Bakelite solution Benzoylamino 6-chloranthraquinone Benzylsulphanilate sodium Bismuth salts Bleaching method for leather with Neradol D Bloom Bromo-[Greek: b]-naphthol Bromonitrophenol Bromophloroglucinol Bromosalicylic acid Bromotrinitrophenol

C

Carbazole Carbomethoxyhydroxybenzoic acid, Carbomethoxyhydroxybenzoic acid chloride, Catechine Catechol Cerium salts Ceruleoellagic acid Cesium salts Chestnut wood extract Chloronaphthalenesulphonic acid Chlorophenol Chrome-Neradol D tannage Chrome salts Chrome tannage Coal, bituminous Coffee tannin Combination tannage with Ordoval Combination tannage with Neradol D Condensation by heat Condensation methods Condensation with aldehydes Condensation with glycerol Condensation with phosphorus compounds Condensation with sulphur chloride Copper salts Corinal Cresol Cresol-p-sulphonic acid, o- Cresolsulphonic acid Cresotinic acid

D

Depsides Detannisation with hide powder Diaminoanthraquinone Diaminonaphthylmethanedisulphonic acid Dianilinoquinone Dibenzopyrrol Di-[Greek: b]-oxynaphthoic Di-[Greek: b]-resorcylic acid Dichloranthraquinone Dichloronaphthylmethanedisulphonic acid Dicresylmethanedisulphonic acid Dicresylmethanedisulphonic acid purified electro-osmotically Dicresylmethane sulphonate sodium Didepsides Didymium salts Diferulic acid Digallic acid Digallic acid, [Greek: b]- Digallic acid, inactive Digallic acid, m- Digalloylleucodigallic acid anhydride Digentisinic acid Dihydric alcohols, aromatic Dihydroxybenzene, m- Dihydroxybenzene, o- Dihydroxybenzene, p- Dihydroxybenzenes Dimethylaniline Dimethylellagic acid Di-m-oxybenzoic acid Dinaphthylmethanedisulphonic acid Dinitronaphthylmethanedisulphonic acid Di-o-cumaric acid Diorsellic acid, o- Diorsellic acid, p- Dioxyellagic acid Dioxynaphthylmethanedisulphonic acid Dioxytoluic acid Diphenylmethane Diphenylmethanedisulphonic acid Di-p-hydroxybenzoic acid Diprotocatechuic acid Disalicylic acid Disyringic acid Dithionaphthylmethanedisulphonic acid Dividivi Dividivi tannin Dixylylmethanedisulphonic acid

E

Electro-chemical behaviour of Neradol D Electro-osmosis of Neradol D Ellagic acid Ellagitannic acid Empirical formula of tannin Erythrine Esco-extract Ester formula of tannin Ethyl acetate figure

F

Fat-Neradol D tannage Feruloyl-p-oxybenzoic acid Flavellagic acid Fluorene Formaldehyde Formaldehyde tannage

G

G-acid Gallate ethyl Gallic acid Galloflavine Galloyl-p-hydroxybenzoic acid Galls, oak Gall tannin Generator tar Guaiacol

H

Halogens Hepta-[tribenzoyl-galloyl]-p-iodophenylmaltosazone Hexahydroxyaurinecarboxylic acid Hexoxyanthraquinone Hexoxydiphenyl Hexoxydiphenyldicarboxylic acid Hexoxydiphenylmethanedicarboxylic acid Humic acid Hydrolysis of tannins Hydroquinone Hydroxybenzoate sodium, m- Hydroxybenzoate sodium, p- Hydroxybenzoic acid, p- Hydroxybenzoic acid Hydroxy-cymenes

I

Indophenol reaction Iron, reaction of, to Neradol D Iron salts

K

Ketone formula of tannin

L

Lanthanum salts Lead salts Leather analysis in presence of Neradol D Lecanoric acid Leucodigallic acid Leucoellagic acid Leucotannin Lignite Luteic acid

M

Malletto tannin Mangrove tannin Melangallic acid Mercury salts Metellagic acid Methylamino-4-bromanthraquinone Methylenedinaphthol Methylenedisalicylic acid Methylenedisalicylic acid, brominated Methylenedisalicylic acid, iodised Methylisopropylphenanthrene Methylotannin Molybdenum figure Monochloro-p-dihydroxybenzene Mud Myrabolams Myrabolams, tannin

N

Naphthalenesulphonic acid, [Greek: b]- Naphthol, [Greek: a]- Naphthol, [Greek: b]- Naphthol-[Greek: a]-methanesulphonic acid Naphtholdisulphonic acid Naphtholmonosulphonic acid Naphtholsulphonic acid, [Greek: a]- Naphtholsulphonic acid, [Greek: b]- Neodymium salts Neradol D Neradol D tannin Neradol N Neradol ND Neradol ND, neutral Nitronaphthalenesulphonic acid Nitrophenol, o- Nitrosodimethylaniline Non-tannins Novolak

O

Oak bark Oak bark tannin Official method of tannin analysis Orcinol Ordoval G Orsellic acid Orsellinoyl-p-oxybenzoic acid Oxyanthraquinone Oxyazo reaction Oxybenzoyl-m-hydroxybenzoic acid Oxybenzoyl-p-hydroxybenzoic acid, m- Oxybenzoylsyringic acid Oxynaphthoyl-p-hydroxybenzoic acid, a- Oxynaphthylmethanesulphonic acid Oxyphenylmethanesulphonic acid Oxyquinoline

P

PATENTS— Austrian 58,405; 61,057; 61,061; 64,479; 66,895; 68,796; 69,194; 69,375; 69,376; 69,377; 70,162 German 72,161; 111,408; 112,183; 132,224; 181,288; 184,449; 200,539; 206,957; 211,403; 262,558; 282,313; 286,568; 290,965; 291,457; 293,042; 293,640; 293,693; 297,187; 297,188; 300,567; 303,640; 305,516; 319,713; 320,613 Swiss 78,282; 78,797; 79,139 U.S.A. 1,639,174 Peat Pelts Pelts, action on, of Neradol D Penta-[p-hydroxybenzoyl] glucose, Penta-[p-methyl-m-digalloyl]-glucose Penta-[pyrogalloylcarboyl]-glucose Pentacetylleucotannin Pentacetyl-m-digallic acid Pentacetyl tannin Pentadigalloylglucose Pentagalloylglucose Pentagalloylglucoside Pentamethyldigallic acid, methyl ester Pentamethyl-m-digalloyl chloride, Pentamethyl-m-digallic acid Pentamethyl-m-digallic acid methyl ester Pentamethyl-p-digallic acid Pentamethyl-p-digallic acid methyl ester Pentamethoxybiphenylmethylolide carboxylic acid methyl ester Pentoxybiphenylmethylolide Pentoxybiphenylmethylolide carboxylic acid Phenanthraquinone Phenolsulphonate sodium Phenolsulphonic acid Phenolsulphonic acid anhydride Phenol, tautomeric Phenylcarboxylic acid Phenylhydrazine derivatives of tannin Phenylhydrazine ellagic acid Phlobaphene Phlobaphene-solubilising action of neradols Phloroglucinol Phthalic acid Pickling Picric acid Platinum salts Polydepsides Polydigalloylleucodigallic acid anhydride Polyhydroxybenzenes Pomegranate Preparation of tannin infusion Properties of leather tanned with Neradol Protocatechuic acid Protocatechuyl-p-hydroxybemoic acid Pseudo-tannage Purpuro tannin Pyrogallol Pyrogallic acid Pyrogalloylcarboyl-p-oxybenzoic acid Pyruvic acid

Q

Quinazarene Quinoline Quinone

R

R-acid Reaction, Procter-Hirst Reagents for Neradol D tannage Resites Resitol Resols Resorcinol Resorcylic acid, [Greek: b]- Retene

Rosins, acid Rosolic acid Rufigallic acid

S

S-acid Salicylic acid Salicylic acid phenyl ester Salicyl-p-hydroxybenzoic acid Salol Silver oxide Solution salt Solvenol Structure of tannin Sulphinic acid Sulphite cellulose extract Sulphite lye Sulphonamide Sulphonic acids, aromatic Sulphonic chloride Sulphur Sulphur tannage Sulphuric acid-free Neradol D Sulphuric acid in leather Syringoyl-p-hydroxybenzoic acid

T

Tannin Tannin action, real Tannin analysis Tanning matters Tannin molecule Tannin, pure Tannophor Test tannage Tetradepsides Tetragalloyl-[Greek: a]-methylglucoside Tetramethylellagic acid Tetroxydiphenyldimethylolide Thionaphtholsulphonic acid Thiosulphonic acid Thorium salts Thymol Toluidoanthraquinone, l-m- Total solids Total solubles Tribromophenol Tribromopyrogallic acid Tricarbomethoxygalloyl chloride Tridepside Trihydroxybenzenes Trinitrophenol Triphenylmethane

V

Valonea Vanadium salts Vanillic acid Vanilloyl-di-p-oxybenzoyl-p-hydroxybenzoic acid Vanilloyl-p-hydroxybenzoic acid Vanilloyl vanillin

X

Xanthenes

Z

Zinc salts Zirconium salts

THE END