These are all available for soap-making.

LESS-KNOWN OILS AND FATS OF LIMITED USE.

Shea Butter.—Shea butter is extracted from the kernels of the Bassia Parkii and exported from Africa and Eastern India. This fat is somewhat tough and sticky, and the amount of unsaponifiable matter present is sometimes considerable. Samples examined by us gave the following data:—

___________ Saponification Acidity Titre, Refractive Equivalent. (as Oleic Acid) deg.C. Index Per Cent. at 60 deg. C. ___ ____ __ ____ 313 8.2 53.2 1.4566 303 7.33 53 1.4558 1.4471 (F. Acids) ___ ____ __ ____

Mowrah-seed Oil.—The mowrah-seed oil now offered for soap-making is derived from the seeds of Bassia longifolia and Bassia latifolia. It is largely exported from India to Belgium, France and England. The following are the results of some analyses made by us:—

Saponification Acidity Titre, Refractive Equivalent. (as Oleic Acid) deg.C. Index at Per Cent. 60 deg. C. 291 10 43.4 1.4518 291.5 7.1 42.7 291.2 9.9 43.8 292 11.26 40.5

Chinese vegetable tallow is the name given to the fat which is found coating the seeds of the "tallow tree" (Stillingia sebifera) which is indigenous to China and has been introduced to India where it flourishes. The following is a typical sample:—

_______ Saponification Acidity Titre, Equivalent Per Cent. deg.C. ___ ___ __ 280.2 5.24 52.5 ___ ___ __

The seeds of the "tallow tree" yield an oil (stillingia oil) having drying properties.

Borneo Tallow.—The kernels of several species of Hopea (or Dipterocarpus), which flourish in the Malayan Archipelago, yield a fat known locally as Tangawang fat. This fat is moulded (by means of bamboo canes) into the form of rolls about 3 inches thick, and exported to Europe as Borneo Tallow.

A sample tested by one of us gave the following data:—

Saponification Acidity Titre, Equivalent. (as Oleic Acid) deg.C. Per Cent. 292 36 50.8

Kapok oil is produced from a tree which is extensively grown in the East and West Indies. The Dutch have placed it on the market and the figures given by Henriques (Chem. Zeit., 17, 1283) and Philippe (Monit. Scient., 1902, 730), although varying somewhat, show the oil to be similar to cotton-seed oil.

VARIOUS NEW FATS AND OILS SUGGESTED FOR SOAP-MAKING.

Carapa or Andiroba oil, derived from the seeds of a tree (Carapa Guianensis) grown in West Indies and tropical America, has been suggested as suitable for soap-making. Deering (Imperial Institute Journ., 1898, 313) gives the following figures:—

Saponification Acidity Melting Point Equivalent Per Cent. of Fatty Acids, deg.C. 287 12 89

Another observer (Rev. Chem. Ind., 13, 116) gives the setting point of the fatty acids as 56.4 deg. C.

Candle-nut oil obtained from the seeds of a tree flourishing in India and also the South Sea Islands.

The following figures have been published:—

Saponi- fication Titre, Iodine No. Observers. References. Equiv- alent.[1] deg.C. 299-304.9 13 136.3-139.3 De Negri Chem. Centr., 1898, p. 493. 291 163.7 Lewkowitsch Chem. Revue, 1901, p. 156. 296 12.5 152.8 Kassler Farben-Zeitung, 1903, p. 359.

Curcas oil is produced in Portugal from the seeds of the "purging nut tree," which is similar to the castor oil plant, and is cultivated in Cape Verde Islands and other Portuguese Colonies.

The following data have been observed:—

_____________ Saponi- fication Titre, Iodine No. Observers. References. Equiv- alent.[2] deg.C. ___ __ __ __ ______ 291.4 0.36 99.5 Archbut _J. S. C. Ind._, 1898, p. 1010. 290.3 4.46 98.3 Lewkowitsch _Chem. Revue_, 1898, p. 211. 283.1 0.68 107.9 Klein _Zeits. angew. Chem._, 1898, p. 1012. ___ __ __ __ ______

The titre is quoted by Lewkowitsch as 28.6 deg. C.

Goa butter or Kokum butter is a solid fat obtained from the seeds of Garcinia indica, which flourishes in India and the East Indies. Crossley and Le Sueur (Journ. Soc. Chem. Industry, 1898, p. 993) during an investigation of Indian oils obtained these results:—

Saponification Acidity Iodine No. Equivalent.[3] Per Cent. 300 7.1 34.2

Safflower oil is extracted from the seeds of the Carthamus tinctorius, which, although indigenous to India and the East Indies, is extensively cultivated in Southern Russia (Saratowa) and German East Africa. Its use has been suggested for soft-soap making. The following figures have been published:—

_____________ Saponi fication Iodine Observers. References. Equiv- No. alent.[4] __ __ __ ___ ______ Average 295.5 141.29 Crossley and _J. S. C. Ind._, 1898, p. 992; of Le Sueur _J. S. C. Ind._, 1900, p. 104. Twelve 287.1 141.6 Shukoff _Chem. Revue_, 1901, p. 250. Samples 289.2 130 Tylaikow _Chem. Revue_, 1902, p. 106. 293.7 142.2 Fendler _Chem. Zeitung_, 1904, p. 867. __ __ __ ___ ______

Maripa fat is obtained from the kernels of a palm tree flourishing in the West Indies, but, doubtless, the commercial fat is obtained from other trees of the same family. It resembles cocoa-nut oil and gives the following figures:—

_____________ Saponi- Melting fication Point Equiv- Iodine of Fatty alent.[5] No. Acids, Observer. Reference. deg.C. __ __ ___ ___ ______ 217 9.49 25 Bassiere _J. S. C. Ind._, 1903, p. 1137. __ __ ___ ___ ______

Niam fat, obtained from the seeds of Lophira alata, which are found extensively in the Soudan. The fat, as prepared by natives, has been examined by Lewkowitsch, and more recently Edie has published the results of an analysis. The figures are as follows:—

_____________ Saponi- fication Titre, Iodine Observers. References. Equiv- No. alent.[6] deg.C. ___ __ __ __ ______ 295.1 78.12 42.5 Lewkowitsch _J. S. C. Ind._, 1907, p. 1266. 287.7 75.3 Edie. _Quart. J. Inst. Comm. Research in Tropics._ ___ __ __ __ ______

Cohune-nut oil is produced from the nuts of the cohune palm, which flourishes in British Honduras. This oil closely resembles cocoa-nut and palm-nut oils and is stated to saponify readily and yield a soap free from odour. The following figures, obtained in the Laboratory of the Imperial Institute, are recorded in the official Bulletin, 1903, p. 25:—

_________ Saponification Iodine No. Melting Point of Equivalent. Fatty Acids, deg.C. ___ __ ____ 253.9-255.3 12.9-13.6 27-30 ___ __ ____

Mafoureira or Mafura tallow from the nuts of the mafoureira tree, which grows wild in Portuguese East Africa. The following figures are published:—

_____________ Saponi- fication Iodine References. Equi- No. valent. ___ ___ ___ ______ Titre, deg.C. 253.8 44-48 46.14 De Negri and Fabris, _Annal. del Lab. Chim. Delle Gabelle_, 1891-2, p. 271. Acidity (as Oleic Acid) Per Cent. _Bulletin Imp. Inst._, 232.8-233.7 21.26 47.8-55.8 1903, p. 27. ___ ___ ___ ______

Pongam oil, obtained from the beans of the pongam tree, which flourishes in East India, has been suggested as available for the soap industry, but the unsaponifiable matter present would militate against its use. Lewkowitsch (Analyst, 1903, pp. 342-44) quotes these results:—

Saponi- fication Iodine Acidity, Unsaponifiable, Equi- No. Per Cent. Per Cent. valent.[7] Oil extracted 315 94 3.05 9.22 in laboratory Indian specimen 306 89.4 0.5 6.96

Margosa oil is obtained from the seeds of Melia azedarach, a tree which is found in most parts of India and Burma.

Lewkowitsch (Analyst, 1903, pp. 342-344) gives these figures:—

Saponification Iodine Titre, Equivalent.[8] No. deg.C. 284.9 69.6 42

Dika fat or Wild Mango oil is obtained from the seed kernels of various kinds of Irvingia by boiling with water. Lemarie (Bulletin Imp. Inst., 1903, p. 206) states that this fat is used in the place of cocoa-nut oil in the manufacture of soap. Lewkowitsch (Analyst, 1905, p. 395) examined a large sample of dika fat obtained from seeds of Irvingia bateri (South Nigeria) and gives the following data:—

_________ Saponification Iodine Titre, Unsaponifiable, Equivalent.[9] No. deg.C. Per Cent. ___ __ __ ____ 229.4 5.2 34.8 0.73 ___ __ __ ____

Baobab-seed Oil.—Balland (Journ. Pharm. Chem., 1904, p. 529, abstracted in Journ. Soc. Chem. Ind., 1905, p. 34) states that the natives of Madagascar extract, by means of boiling water, from the seeds of the baobab tree, a whitish solid oil, free from rancidity, and possessed of an odour similar to Tunisian olive oil. He suggests that it may, with advantage, replace cocoa-nut oil in soap manufacture.

Persimmon-seed Oil.—Lane (J. S. C. Ind., 1905, p. 390) gives constants for this oil which he describes as semi-drying, of brownish yellow colour, and having taste and odour like pea-nut (arachis) oil. The following are taken from Lane's figures:—

_______ Saponification Iodine Titre, Equivalent.[10] No. deg.C. ____ __ __ 298.4 115.6 20.2 ____ __ __

Wheat oil, extracted from the wheat germ by means of solvents, has been suggested as applicable for soap-making (H. Snyder, abstr. J. S. C. Ind., 1905, p. 1074). The following figures have been published:—

Saponi- fication Acidity, Iodine Titre, Observers. References. Equiv- Per No. alent.[11] Cent. deg.C. 306 5.65 115.17 29.7 De Negri. Chem. Zeit., 1898 (abstr. J. S. C. I., 1898, p. 1155). 297 20 115.64 Frankforter J. Amer. C. Soc., & Harding 1899, 758-769 (abstr. in J. S. C. I., 1899, p. 1030).

Tangkallah fat, from the seeds of a tree growing in Java and the neighbouring islands, is suitable for soap-making. Schroeder (Arch. Pharm., 1905, 635-640, abstracted in J. S. C. Ind., 1906, p. 128) gives these values:—

Saponification Acidity, Iodine Unsaponifiable, Equivalent.[12] Per Cent. No. Per Cent. 209 1.67 2.28 1.44

It is a hard fat, nearly white, possessing neither taste nor characteristic odour and solidifying at about 27 deg. C.

Oil of Inoy-kernel.—(Bulletin Imp. Inst., 1906, p. 201). The seeds of Poga oleosa from West Africa yield on extraction an oil which gives the figures quoted below, and is suggested as a soap-maker's material:—

Saponification Iodine Titre, Equivalent. No. deg.C. 304 89.75 22

ROSIN.

Rosin is the residuum remaining after distillation of spirits of turpentine from the crude oleo-resin exuded by several species of the pine, which abound in America, particularly in North Carolina, and also flourish in France and Spain. The gigantic forests of the United States consist principally of the long-leaved pine, Pinus palustris (Australis), whilst the French and Spanish oleo-resin is chiefly obtained from Pinus pinaster, which is largely cultivated.

Rosin is a brittle, tasteless, transparent substance having a smooth shining fracture and melting at about 135 deg. C. (275 deg. F.). The American variety possesses a characteristic aromatic odour, which is lacking in those from France and Spain. It is graded by samples taken out of the top of every barrel, and cut into 7/8 of an inch cubes, which must be uniform in size—the shade of colour of the cube determines its grade and value.

The grades are as follows:—

W. W. (Water white.) W. G. (Window glass.) N. (Extra pale.) M. (Pale.) K. (Low pale.) I. (Good No. 1.) H. (No. 1.) G. (Low No. 1.) F. (Good No. 2.) E. (No. 2.) D. (Good strain.) C. (Strain.) B. (Common strain.) A. (Common.)

Unsaponifiable matter is present in rosin in varying amounts.

Below are a few typical figures taken from a large number of collated determinations:—

___________ Saponification Total Free Iodine Equivalent. Acid No. Acid No. No. ___ ___ __ __ __ American W. W. 330.5 169.7 119.1 126.9 American N. 312.3 179.6 161.4 137.8 French 320.5 175 168 120.7 Spanish 313.4 179 160 129.8 ___ ___ __ __ __

ALKALI (CAUSTIC AND CARBONATED).

The manufacture of alkali was at one time carried on in conjunction with soap-making, but of late years it has become more general for the soap manufacturer to buy his caustic soda or carbonated alkali from the alkali-maker.

Although there are some alkali-makers who invoice caustic soda and soda ash in terms of actual percentage of sodium oxide (Na_{2}O), it is the trade custom to buy and sell on what is known as the English degree, which is about 1 per cent. higher than this.

The English degree is a survival of the time when the atomic weight of sodium was believed to be twenty-four instead of twenty-three, and, since the error on 76 per cent. Na_{2}O due to this amounts to about 1 per cent., may be obtained by adding this figure to the sodium oxide really present.

_Caustic soda_ (sodium hydrate) comes into commerce in a liquid form as 90 deg. Tw. (and even as high as 106 deg. Tw.), and other degrees of dilution, and also in a solid form in various grades as 60 deg., 70 deg., 76-77 deg., 77-78 deg. These degrees represent the percentage of sodium oxide (Na_{2}O) present plus the 1 per cent. The highest grade, containing as it does more available caustic soda and less impurities, is much more advantageous in use.

Carbonate of soda or soda ash, 58 deg., also termed "light ash," and "refined alkali". This is a commercially pure sodium carbonate containing about 0.5 per cent. salt (NaCl). The 58 deg. represents the English degrees and corresponds to 99 per cent. sodium carbonate (Na{2}CO{3}).

Soda ash, 48 deg., sometimes called "caustic soda ash," often contains besides carbonate of soda, 4 per cent. caustic soda (sodium hydrate), and 10 per cent. salt (sodium chloride), together with water and impurities.

The 48 degrees refers to the amount of alkali present in terms of sodium oxide (Na_{2}O), but expressed as English degrees.

Caustic potash (potassium hydrate) is offered as a liquid of 50-52 deg. B. (98-103 deg. Tw.) strength, and also in solid form as 75-80 deg. and 88-92 deg. The degrees in the latter case refer to the percentage of potassium hydrate (KHO) actually present.

Carbonate of Potash.—The standard for refined carbonate of potash is 90-92 per cent. of actual potassium carbonate (K{2}CO{3}) present, although it can be obtained testing 95-98 per cent.

OTHER MATERIALS.

Water.—Water intended for use in soap-making should be as soft as possible. If the water supply is hard, it should be treated chemically; the softening agents may be lime and soda ash together, soda ash alone, or caustic soda. There are many excellent plants in vogue for water softening, which are based on similar principles and merely vary in mechanical arrangement. The advantages accruing from the softening of hard water intended for steam-raising are sufficiently established and need not be detailed here.

Salt (sodium chloride or common salt, NaCl) is a very important material to the soap-maker, and is obtainable in a very pure state.

Brine, or a saturated solution of salt, is very convenient in soap-making, and, if the salt used is pure, will contain 26.4 per cent. sodium chloride and have a density of 41.6 deg. Tw. (24.8 deg. B.).

The presence of sulphates alters the density, and of course the sodium chloride content.

Salt produced during the recovery of glycerine from the spent lyes often contains sulphates, and the density of the brine made from this salt ranges higher than 42 deg. Tw. (25 deg. B.).

Soapstock.—This substance is largely imported from America, where it is produced from the dark-coloured residue, termed mucilage, obtained from the refining of crude cotton-seed oil. Mucilage consists of cotton-seed oil soap, together with the colouring and resinous principles separated during the treatment of the crude oil. The colouring matter is removed by boiling the mucilage with water and graining well with salt; this treatment is repeated several times until the product is free from excess of colour, when it is converted into soap and a nigre settled out from it.

Soapstock is sold on a fatty acid basis; the colour is variable.

FOOTNOTES:

[1] Calculated by us from saponification value.

[2] Calculated by us from saponification value.

[3] Calculated by us from saponification value.

[4] Calculated by us from saponification value.

[5] Calculated by us from saponification value.

[6] Calculated by us from saponification value.

[7] Calculated by us from saponification value.

[8] Calculated by us from saponification value.

[9] Calculated by us from saponification value.

[10] Calculated by us from saponification value.

[11] Calculated by us from saponification value.

[12] Calculated by us from saponification value.



CHAPTER IV.

BLEACHING AND TREATMENT OF RAW MATERIALS INTENDED FOR SOAP-MAKING.

Palm Oil—Cotton-seed Oil—Cotton-seed "Foots"—Vegetable Oils—Animal Fats—Bone Fat—Rosin.

Having described the most important and interesting oils and fats used or suggested for use in the manufacture of soap, let us now consider briefly the methods of bleaching and treating the raw materials, prior to their transference to the soap-pan.

Crude Palm Oil.—Of the various methods suggested for bleaching palm oil, the bichromate process originated by Watts is undoubtedly the best. The reaction may be expressed by the following equation, though in practice it is necessary to use twice the amount of acid required by theory:—

K{2}Cr{2}O{7} + 14HCl = 2KCl + Cr{2}Cl{6} + 7H{2}O + 6Cl.

6Cl + 3H_{2}O = 6HCl + 3O.

The palm oil, freed from solid impurities by melting and subsidence, is placed in the bleaching tank, and washed with water containing a little hydrochloric acid. Having allowed it to rest, and drawn off the liquor and sediment (chiefly sand), the palm oil is ready for treatment with the bleaching reagent, which consists of potassium bichromate and commercial muriatic acid. For every ton of oil, 22 to 28 lb. potassium bichromate and 45 to 60 lb. acid will be found sufficient to produce a good bleached oil.

The best procedure is to act upon the colouring matter of the oil three successive times, using in the first two treatments one-third of the average of the figures just given, and in the final treatment an appropriate quantity which can be easily gauged by the appearance of a cooled sample of the oil.

The potassium bichromate is dissolved in hot water and added to the crude palm oil, previously heated to 125 deg. F. (52 deg. C.), the requisite amount of muriatic acid being then run in and the whole well agitated by means of air. The bright red colour of the oil gradually changes to dark brown, and soon becomes green. The action having proceeded for a few minutes, agitation is stopped, and, after allowing to settle, the green liquor is withdrawn.

When sufficiently bleached the oil is finally washed (without further heating) with hot water (which may contain salt), to remove the last traces of chrome liquor.

If the above operation is carried out carefully, the colouring matter will be completely oxidised.

It is important, however, that the temperature should not be allowed to rise above 130 deg. F. (54 deg. C.) during the bleaching of palm oil, otherwise the resultant oil on saponification is apt to yield a soap of a "foxy" colour. The bleached oil retains the characteristic violet odour of the original oil.

It has been suggested to use dilute sulphuric acid, or a mixture of this and common salt, in the place of muriatic acid in the above process.

Crude Cotton-seed Oil.—The deep colouring matter of crude cotton-seed oil, together with the mucilaginous and resinous principles, are removed by refining with caustic soda lye.

The chief aim of the refiner is to remove these impurities without saponifying any of the neutral oil. The percentage of free fatty acids in the oil will determine the quantity of caustic lye required, which must only be sufficient to remove this acidity.

Having determined the amount of free acidity, the quantity of caustic soda lye necessary to neutralise it is diluted with water to 12 deg. or 15 deg. Tw. (8 deg. or 10 deg. B.), and the refining process carried out in three stages. The oil is placed in a suitable tank and heated by means of a closed steam coil to 100 deg. F. (38 deg. C.), a third of the necessary weak caustic soda lye added in a fine stream or by means of a sprinkler, and the whole well agitated with a mechanical agitator or by blowing a current of air through a pipe laid on the bottom of the tank.

Prolonged agitation with air has a tendency to oxidise the oil, which increases its specific gravity and refractive index, and will be found in the soap-pan to produce a reddish soap. As the treatment proceeds, the temperature may be carefully raised, by means of the steam coil, to 120 deg. F. (49 deg. C.).

The first treatment having proceeded fifteen minutes, the contents of the tank are allowed to rest; the settling should be prolonged as much as possible, say overnight, to allow the impurities to precipitate well, and carry down the least amount of entangled oil. Having withdrawn these coloured "foots," the second portion of the weak caustic soda solution is agitated with the partially refined oil, and, when the latter is sufficiently treated, it is allowed to rest and the settled coloured liquor drawn off as before. The oil is now ready for the final treatment, which is performed in the same manner as the two previous ones. On settling, a clear yellow oil separates.

If desired, the oil may be brightened and filtered, after refining to produce a marketable article, but if it is being refined for own use in the soap-house, this may be omitted.

The residue or "foots" produced during the refining of crude cotton-seed oil, known in the trade as "mucilage," may be converted into "soapstock" as mentioned in the preceding chapter, or decomposed by a mineral acid and made into "black grease" ready for distillation by superheated steam.

Vegetable Oils.—The other vegetable oils come to the soap-maker's hand in a refined condition; occasionally, however, it is desirable to remove a portion of the free fatty acids, which treatment also causes the colouring matter to be preciptated. This is effected by bringing the oil and a weak solution of caustic lye into intimate contact. Cocoa-nut oil is often treated in this manner. Sometimes it is only necessary to well agitate the oil with 1-1/2 per cent. of its weight of a 12 deg. Tw. (8 deg. B.) solution of caustic soda and allow to settle. The foots are utilised in the soap-pan.

Animal Fats.—Tallows are often greatly improved by the above alkaline treatment at 165 deg. F. (73 deg. C.). It is one of the best methods and possesses advantages over acid processes—the caustic soda removes the free acid and bodies of aldehyde nature, which are most probably the result of oxidation or polymerisation, whereas the neutral fat is not attacked, and further, the alkaline foots can be used in the production of soap.

Bone fat often contains calcium (lime) salts, which are very objectionable substances in a soap-pan. These impurities must be removed by a treatment with hydrochloric or sulphuric acid. The former acid is preferable, as the lime salt formed is readily soluble and easily removed. The fat is agitated with a weak solution of acid in a lead-lined tank by blowing in steam, and when the treatment is complete and the waste liquor withdrawn, the last traces of acid are well washed out of the liquid fat with hot water.

Rosin.—Several methods have been suggested for bleaching rosin; in some instances the constitution of the rosin is altered, and in others the cost is too great or the process impracticable.

The aim of these processes must necessarily be the elimination of the colouring matter without altering the original properties of the substance. This is best carried out by converting the rosin into a resinate of soda by boiling it with a solution of either caustic soda or carbonated alkali. The process is commenced by heating 37 cwt. of 17 deg. Tw. (11 deg. B.) caustic soda lye, and adding 20 cwt. of rosin, broken into pieces, and continuing the boiling until all the resinate is homogeneous, when an addition of 1-1/2 cwt. of salt is made and the boiling prolonged a little. On resting, the coloured liquor rises to the surface of the resinate, and may be siphoned off (or pumped away through a skimmer pipe) and the resinate further washed with water containing a little salt.

The treatment with carbonated alkali is performed in a similar manner. A solution, consisting of 2-3/4 cwt. of soda ash (58 deg.), in about four times its weight of water, is heated and 20 cwt. of rosin, broken into small pieces, added. The whole is heated by means of the open steam coil, and care must be taken to avoid boiling over. Owing to the liberation of CO_{2} gas, frothing takes place. A large number of patents have been granted for the preparation of resinate of soda, and many methods devised to obviate the boiling over. Some suggest mixing the rosin and soda ash (or only a portion of the soda ash) prior to dissolving in water; others saponify in a boiler connected with a trap which returns the resinate to the pan and allows the carbonic-acid gas to escape or to be collected.

With due precaution the method can be easily worked in open vessels, and, using the above proportions, there will be sufficient uncombined rosin remaining to allow the resultant product to be pumped into the soap with which it is intended to intermix it, where it will be finally saponified thoroughly.

The salt required, which, in the example given, would be 1-1/2 cwt., may be added to the solution prior to the addition of rosin or sprinkled in towards the finish of the boiling. When the whole has been sufficiently boiled and allowed to rest, the liquor containing the colouring matter will float over the resinate, and, after removal, may be replaced by another washing.

Many other methods have been suggested for the bleaching, refining and treatment of materials intended for saponification, but the above practical processes are successfully employed.

All fats and oils after being melted by the aid of steam must be allowed to thoroughly settle, and the condensed water and impurities withdrawn through a trap arrangement for collecting the fatty matter. The molten settled fatty materials en route to the soap-pan should be passed through sieves sufficiently fine to free them from suspended matter.



CHAPTER V.

SOAP-MAKING.

Classification of Soaps—Direct Combination of Fatty Acids with Alkali—Cold Process Soaps—Saponification under Increased or Diminished Pressure—Soft Soap—Marine Soap—Hydrated Soaps, Smooth and Marbled—Pasting or Saponification—Graining Out—Boiling on Strength—Fitting—Curd Soaps—Curd Mottled—Blue and Grey Mottled Soaps—Milling Base—Yellow Household Soaps—Resting of Pans and Settling of Soap—Utilisation of Nigres—Transparent Soaps—Saponifying Mineral Oil—Electrical Production of Soap.

Soaps are generally divided into two classes and designated "hard," and "soft," the former being the soda salts, and the latter potash salts, of the fatty acids contained in the material used.

According to their methods of manufacture, soaps may, however, be more conveniently classified, thus:—

(A) Direct combination of fatty acids with alkali.

(B) Treatment of fat with definite amount of alkali and no separation of waste lye.

(C) Treatment of fat with indefinite amount of alkali and no separation of waste lye.

(D) Treatment of fat with indefinite amount of alkali and separation of waste lye.

(A) Direct Combination of Fatty Acids with Alkali.—This method consists in the complete saturation of fatty acids with alkali, and permits of the use of the deglycerised products mentioned in chapter ii., section 2, and of carbonated alkalies or caustic soda or potash. Fatty acids are readily saponified with caustic soda or caustic potash of all strengths.

The saponification by means of carbonated alkali may be performed in an open vat containing a steam coil, or in a pan provided with a removable agitator.

It is usual to take soda ash (58 deg.), amounting to 19 per cent. of the weight of fatty acids to be saponified, and dissolve it in water by the aid of steam until the density of the solution is 53 deg. Tw. (30 deg. B.); then bring to the boil, and, whilst boiling, add the molten fatty acids slowly, but not continuously.

Combination takes place immediately with evolution of carbonic acid gas, which causes the contents of the vat or pan to swell, and frequently to boil over. The use of the agitator, or the cessation of the flow of fatty acids, will sometimes tend to prevent the boiling over. It is imperative that the steam should not be checked but boiling continued as vigorously as possible until all the alkali has been absorbed and the gas driven off.

The use of air to replace steam in expelling the carbonic acid gas has been patented (Fr. Pat. 333,974, 1903).

A better method of procedure, however, is to commence with a solution of 64 deg. Tw. (35 deg. B.) density, made from half the requisite soda ash (9-1/2 per cent.), and when this amount of alkali has all been taken up by the fatty acids (which have been added gradually and with continuous boiling), the remaining quantity of soda ash is added in a dry state, being sprinkled over each further addition of fatty acid.

This allows the process to be more easily controlled and boiling over is avoided.

It is essential that the boiling by steam should be well maintained throughout the process until all carbonic acid gas has been thoroughly expelled; when that point is reached, the steam may be lessened and the contents of the vat or pan gently boiled "on strength" with a little caustic lye until it ceases to absorb caustic alkali, the soap being finished in the manner described under (D).

It is extremely difficult to prevent discoloration of fatty acids, hence the products of saponification in this way do not compare favourably in appearance with those produced from the original neutral oil or fat.

(B) Treatment of Fat with Definite Amount of Alkali and no Separation of Waste Lye.—Cold-process soap is a type of this class, and its method of production is based upon the characteristic property which the glycerides of the lower fatty acids (members of the cocoa-nut-oil class) possess of readily combining with a strong caustic soda solution at a low temperature, and evolving sufficient heat to complete the saponification.

Sometimes tallow, lard, cotton-seed oil, palm oil and even castor oil are used in admixture with cocoa-nut oil. The process for such soap is the same as when cocoa-nut oil is employed alone, with the slight alteration in temperature necessary to render the fats liquid, and the amount of caustic lye required will be less. Soaps made of these blends closely resemble, in appearance, milled toilet soaps. In such mixtures the glycerides of the lower fatty acids commence the saponification, and by means of the heat generated induce the other materials, which alone would saponify with difficulty or only with the application of heat, to follow suit.

It is necessary to use high grade materials; the oils and fats should be free from excess of acidity, to which many of the defects of cold-process soaps may be traced. Owing to the rapidity with which free acidity is neutralised by caustic soda, granules of soap are formed, which in the presence of strong caustic lye are "grained out" and difficult to remove without increasing the heat; the soap will thus tend to become thick and gritty and sometimes discoloured.

The caustic lye should be made from the purest caustic soda, containing as little carbonate as possible; the water used for dissolving or diluting the caustic soda should be soft (i.e., free from calcium and magnesium salts), and all the materials carefully freed from particles of dirt and fibre by straining.

The temperature, which, of course, must vary with the season, should be as low as is consistent with fluidity, and for cocoa-nut oil alone may be 75 deg. F. (24 deg. C.), but in mixtures containing tallow 100 deg. to 120 deg. F. (38 deg. to 49 deg. C.).

The process is generally carried out as follows:—

The fluid cocoa-nut oil is stirred in a suitable vessel with half its weight of 71.4 deg. Tw. (38 deg. B.) caustic soda lye at the same temperature, and, when thoroughly mixed, the pan is covered and allowed to rest. It is imperative that the oils and fats and caustic lye should be intimately incorporated or emulsified. The agitating may be done mechanically, there being several machines specially constructed for the purpose. In one of the latest designs the caustic lye is delivered through a pipe which rotates with the stirring gear, and the whole is driven by means of a motor.

The agitation being complete, chemical action takes place with the generation of heat, and finally results in the saponification of the fats.

At first the contents of the pan are thin, but in a few hours they become a solid mass. As the process advances the edges of the soap become more transparent, and when the transparency has extended to the whole mass, the soap is ready, after perfuming, to be framed and crutched.

The admixture of a little caustic potash with the caustic soda greatly improves the appearance of the resultant product, which is smoother and milder.

The glycerine liberated during the saponification is retained in the soap.

Although it is possible, with care, to produce neutral soaps of good appearance and firm touch by this method, cold-process soaps are very liable to contain both free alkali and unsaponified fat, and have now fallen considerably into disrepute.

Saponification under Increased or Diminished Pressure.—Soaps made by boiling fats and oils, under pressure and in vacuo, with the exact quantity of caustic soda necessary for complete combination, belong also to this class. Amongst the many attempts which have at various times been made to shorten the process of soap-making may be mentioned Haywood's Patent No. 759, 1901, and Jourdan's French Patent No. 339,154, 1903.

In the former, saponification is carried out in a steam-jacketed vacuum chamber provided with an elaborate arrangement of stirrers; in the other process fat is allowed to fall in a thin stream into the amount of lye required for saponification, previously placed in the saponification vessel, which is provided with stirring gear.

When the quantities have been added, steam is admitted and saponification proceeds.

(C) Treatment of Fat with Indefinite Amount of Alkali and no Separation of Waste Lye.—Soft soap is representative of this class. The vegetable fluid oils (linseed, olive, cotton-seed, maize) are for the most part used in making this soap, though occasionally bone fats and tallow are employed. Rosin is sometimes added, the proportion ranging, according to the grade of soap required, from 5 to 15 per cent. of the fatty matter.

The Soft Soap Manufacturers' Convention of Holland stipulate that the materials used in soft-soap making must not contain more than 5 per cent. rosin; it is also interesting to note that a patent has been granted (Eng. Pat. 17,278, 1900) for the manufacture of soft soap from material containing 50 per cent. rosin.

Fish or marine animal oils—whale, seal, etc., once largely used as raw material for soft soap, have been superseded by vegetable oils.

The materials must be varied according to the season; during hot weather, more body with a less tendency to separate is given by the introduction of oils and fats richer in stearine; these materials also induce "figging".

The most important material, however, is the caustic potash lye which should average 40 deg. Tw. (24 deg. B.), i.e., if a weak solution is used to commence saponification, a stronger lye must be afterwards employed to avoid excess of water in the soap, and these average 40 deg. Tw. (24 deg. B.). The potash lye must contain carbonates, which help to give transparency to the resultant soap. If the lye is somewhat deficient in carbonates, they may be added in the form of a solution of refined pearl ash (potassium carbonate).

Caustic soda lye is sometimes admixed, to the extent of one-fourth, with potash lye to keep the soap firmer during hot weather, but it requires great care, as a slight excess of soda gives soft soap a bad appearance and a tendency to separate.

The process is commenced by running fatty matter and weak potash lyes into the pan or copper, and boiling together, whilst the introduction of oil and potash lye is continued.

The saponification commences when an emulsion forms, and the lye is then run in more quickly to prevent the mass thickening.

Having added sufficient "strength" for complete saponification, the boiling is continued until the soap becomes clear.

The condition of the soap is judged by observing the behaviour of a small sample taken from the pan and dropped on glass or iron. If the soap is satisfactory it will set firm, have a short texture and slightly opaque edge, and be quite clear when held towards the light. If the cooled sample draws out in threads, there is an excess of water present. If an opaque edge appears and vanishes, the soap requires more lye. If the sample is turbid and somewhat white, the soap is too alkaline and needs more oil.

The glycerine liberated during saponification is contained in the soap and no doubt plays a part in the production of transparency.

Hydrated soaps, both smooth and marbled, are included in this classification, but are soda soaps. Soap made from cocoa-nut oil and palm-kernel oil will admit of the incorporation of large quantities of a solution of either salt, carbonate of soda, or silicate of soda, without separation, and will retain its firmness. These materials are, therefore, particularly adapted for the manufacture of marine soaps, which often contain as much as 80 per cent. of water, and, being soluble in brine, are capable of use in sea-water. For the same reason, cocoa-nut oil enters largely into the constitution of hydrated soaps, but the desired yield or grade of soap allows of a variation in the choice of materials. Whilst marine soap, for example, is usually made from cocoa-nut oil or palm-kernel oil only, a charge of 2/3 cocoa-nut oil and 1/3 tallow, or even 2/3 tallow and 1/3 cocoa-nut oil, will produce a paste which can carry the solutions of silicate, carbonate, and salt without separation, and yield a smooth, firm soap.

The fatty materials, carefully strained and freed from particles of dirt and fibre, are boiled with weak caustic soda lye until combination has taken place. Saponification being complete, the solution of salt is added, then the carbonate of soda solution, and finally the silicate of soda solution, after which the soap is boiled. When thoroughly mixed, steam is shut off, and the soap is ready for framing.

The marbled hydrated soap is made from cocoa-nut oil or a mixture of palm-kernel oil and cocoa-nut oil with the aid of caustic soda lye 32-1/2 deg. Tw. (20 deg. B.). As soon as saponification is complete, the brine and carbonate of soda solution are added, and the pan allowed to rest.

The soap is then carefully tasted as to its suitability for marbling by taking samples and mixing with the colouring solution (ultramarine mixed with water or silicate of soda solution). If the sample becomes blue throughout, the soap is too alkaline; if the colour is precipitated, the soap is deficient in alkali. The right point has been reached when the marbling is distributed evenly. Having thus ascertained the condition of the pan, and corrected it if necessary, the colour, mixed in water or in silicate of soda solution, is added and the soap framed.

(D) Treatment of Fat with Indefinite Amount of Alkali and Separation of Waste Lye.—This is the most general method of soap-making. The various operations are:—

(a) Pasting or saponification. (b) Graining out or separation. (c) Boiling on strength.

And in the case of milling soap base and household soaps,

(d) Fitting.

(a) Pasting or Saponification.—The melted fats and oils are introduced into the soap-pan and boiled by means of open steam with a caustic soda lye 14 deg. to 23.5 deg. Tw. (10 deg. to 15 deg. B.). Whether the fatty matters and alkali are run into the pan simultaneously or separately is immaterial, provided the alkali is not added in sufficient excess to retard the union.

The commencement of the saponification is denoted by the formation of an emulsion. Sometimes it is difficult to start the saponification; the presence of soap will often assist this by emulsifying the fat and thus bringing it into intimate contact with the caustic soda solution.

When the action has started, caustic soda lye of a greater density, 29 deg. to 33 deg. Tw. (18 deg. to 20 deg. B.), is frequently added, with continued boiling, in small quantities as long as it is being absorbed, which is ascertained by taking out samples from time to time and examining them.

There should be no greasiness in the sample, but when pressed between finger and thumb it must be firm and dry.

Boiling is continued until the faint caustic taste on applying the cooled sample to the tongue is permanent, when it is ready for "graining out". The pasty mass now consists of the soda salts of the fat (as imperfect soap, probably containing emulsified diglycerides and monoglycerides), together with water, in which is dissolved the glycerine formed by the union of the liberated glyceryl radicle from the fat with the hydroxyl radicle of the caustic soda, and any slight excess of caustic soda and carbonates. The object of the next operation is to separate this water (spent lye) from the soap.

(b) Graining Out or Separation.—This is brought about by the use of common salt, in a dry form or in solution as brine, or by caustic soda lye. Whilst the soap is boiling, the salt is spread uniformly over its surface, or brine 40 deg. Tw. (24 deg. B.) is run in, and the whole well boiled together. The soap must be thoroughly boiled after each addition of salt, and care taken that too large a quantity is not added at once.

As the soap is gradually thrown out of solution, it loses its smooth transparent appearance, and becomes opaque and granular.

When a sample, taken out on a wooden trowel, consists of distinct grains of soap and a liquid portion, which will easily separate, sufficient salt or brine has been added; the boiling is stopped and the spent lye allowed to settle out, whilst the soap remains on the surface as a more or less thick mass.

The separated spent lye consists of a solution of common salt, glycerine, and alkaline salts; the preparation of crude glycerine therefrom is considered in chapter ix.

The degree of separation of water (spent lye) depends upon the amount of precipitant used. The aim is to obtain a maximum amount of spent lye separated by the use of a minimum quantity of salt.

The amount of salt required for "graining out" varies with the raw material used. A tallow soap is the most easily grained, more salt is required for cotton-seed oil soap, whereas soaps made from cocoa-nut and palm-kernel oils require very large amounts of salt to grain out thoroughly. Owing to the solubility in weak brine of these latter soaps, it is preferable to grain them with caustic soda lye. This is effected by adding, during boiling, sufficient caustic lye (32-1/2 deg. Tw., 20 deg. B.) to produce the separation of the granules of soap. The whole is allowed to rest; the separated half-spent lye is withdrawn and may be used for the pasting of fresh materials.

After the removal of the settled lye, the grained mass is boiled with sufficient water to dissolve the grain and make it smooth ("close" it), and is now ready for the next operation of "boiling on strength".

(c) Boiling on Strength or Clear Boiling.—This is the most important operation and is often termed "making the soap". The object is to harden the soap and to ensure complete saponification.

Caustic soda lye (32-1/2 deg. Tw., 20 deg. B.) is gradually added until the soap is again opened or grained, and boiling continued by the use of the dry steam coil. As soon as the caustic soda lye is absorbed, another portion is slowly added, and this is continued until the caustic soda or "strength" remains permanent and the soapy mass, refusing to absorb more, is thrown out of solution and grained. The granular mass will boil steadily, and the boiling should be prolonged, as the last traces of neutral oil are difficult to completely saturate with alkali. Thorough saponification takes place gradually, and the operation cannot be hurried; special care has to be bestowed upon this operation to effect the complete combination of fat and alkali.

After resting for several hours, half-spent lye settles to the bottom of the pan. In the case of yellow soaps or milling bases the settled lye is removed to a suitable receptacle and reserved for use in the saponification of other material, and the soap is then ready for the final operation of "fitting".

(d) Fitting.—If the operations just described have been properly performed, the fitting should present no difficulty. The soap is boiled with open steam, and water added until the desired degree of closing is attained. As the water is thoroughly intermixed throughout the mass the thick paste gradually becomes reduced to a smooth, thin consistence. Samples are tested from time to time as to their behaviour in dropping off a hot trowel held sideways; the thin layer should drop off in two or three flakes and leave the surface of the trowel clean and dry. The soap is then in a condition to allow the impurities to gravitate. According to the required soap, the fit may be "coarse" ("open") when the flakes drop off the trowel readily, or "fine" ("close") when the flakes only leave the trowel with difficulty.

If the dilution with water has been allowed to proceed too far, and too fine a fit is produced, which would be denoted by the layer of soap not leaving the trowel, a little caustic lye or brine may be very carefully added and the whole well boiled until the desired condition is obtained.

A good pressure of steam is now applied to the pan, causing the contents to swell as high as possible, this greatly facilitating the settling of impurities; steam is then turned off, the pan covered, and the boil allowed to rest for several days.

The art of fitting consists in leaving the contents of the pan in such a condition that, on standing, all the impurities precipitate, and the settled soap, containing the correct amount of water, is clear and bright.

The above is a general practical outline of the ordinary soap-boiling process. It may be modified or slightly altered according to the fancy of the individual soap-maker or the particular material it is desired to use. Fats and oils not only vary in the amount of alkali they absorb during saponification, but also differ in the strength of the alkali they require. Tallow and palm oil require lye of a density of 15 deg. to 18 deg. Tw. (10 deg. to 12 deg. B.), but cocoa-nut oil alone would not saponify unless the lye was more concentrated, 33 deg. to 42 deg. Tw. (20 deg. to 25 deg. B.). Cotton-seed oil requires weak lyes for saponification, and, being difficult to saponify alone even with prolonged boiling, is generally mixed with animal fat.

When fats are mixed together, however, their varying alkali requirements become modified, and once the saponification is begun with weak lye, other materials are induced to take up alkali of a strength with which alone they would not combine.

It is considered the best procedure to commence the pasting or saponification with weak lye.

In order to economise tank space, it is the general practice to store strong caustic lye (60 deg. to 70 deg. Tw., 33 deg. to 37 deg. B.) and to dilute it as it is being added to the soap-pan by the simultaneous addition of water.

Many manufacturers give all their soap a "brine wash" to remove the last traces of glycerine and free the soap from carbonates. This operation takes place prior to "fitting"; sufficient water is added to the boiling soap to "close" it and then brine is run in to "grain" it.

After resting, the liquor is withdrawn.

Having described the necessary operations in general, we will now consider their application to the preparation of various kinds of hard soap.

Curd Soaps.—Tallow is largely used in the manufacture of white curd soaps, but cocoa-nut oil sometimes enters into their composition.

The first three operations above described, viz., pasting, graining out, and boiling on strength, are proceeded with; the clear boiling by means of a closed steam coil is continued until the "head" is boiled out and the soap is free from froth. A sample taken and cooled should be hard. Boiling is then stopped, and, after covering, the pan is allowed to rest for eight to ten hours, when the soap is ready for filling into frames, where it is crutched until perfectly smooth.

Curd mottled is usually made from melted kitchen stuff and bone grease.

Its preparation is substantially the same as for curd soap, but the clear boiling is not carried so far. The art of curd mottled soap-making lies in the boiling. If boiled too long the mottling will not form properly, and, on the other hand, insufficient boiling will cause the soap to contain an excess of entangled lye. Having boiled it to its correct concentration the pan is allowed to rest about two hours, after which the soap is ready for framing, which should be done expeditiously and the frames covered up.

Some lye, containing the impurities from the fats used, remains in the interstices of the curd, unable to sink, and as the soap cools it is enclosed and forms the mottling. The mottling may, therefore, be considered as a crystallisation of the soap, in which the impurity forms the colour.

Blue and Grey Mottled Soaps.—These are silicated or liquored soaps in which the natural mottling, due to the impure materials used in the early days of soap-making, is imitated by artificial mottling, and are, consequently, entirely different to curd mottled soaps.

The materials employed in making mottled soap comprise bleached palm oil, tallow, bone fat, cocoa-nut oil, palm-kernel oil, cotton-seed oil, and, in some instances, rosin.

The choice of a charge will naturally depend upon the cost; the property of absorbing a large amount of liquor, which is characteristic of soaps made from cocoa-nut oil and palm-kernel oil, is taken advantage of, as are also the physical properties of the various fats and oils, with a view to the crystallisation of the resultant soap and the development of the mottle. The fat is saponified, grained and boiled on strength, as previously described. After withdrawing the half-spent lye, the soap is just closed by boiling with water, and is then ready for the silicate or other saline additions.

Soap intended to be liquored with silicate of soda should be distinctly strong in free alkali; the crystalline nature of the soap is increased thereby, and the mottled effect intensified. Some makers, however, fit the soap coarsely and allow a nigre to deposit; then, after removing the nigre, or transferring the settled soap to another copper, containing scraps of mottled soap, get the soap into a condition for mottling, and add the silicate of soda solution. To every 1 cwt. of soap, 28 lb. of silicate of soda solution, 32-1/2 deg. Tw. (20 deg. B.) is added, whilst boiling; the strength of the silicate solution, however, will depend upon the proportion of cocoa-nut oil and palm-kernel oil present in the charge. Many soap-makers use 20 deg. Tw. (13 deg. B.) (cold) silicate solution, whilst others prefer 140 deg. Tw. (59.5 deg. B.), with the gradual addition of water to the soap, kept boiling, until the product is in the correct mottling condition, and others, again, use bleach liquor, soda crystals, pearl ash, and salt, together with silicate solution.

Considerable skill and experience is necessary to discern when the soap acquires the correct mottling state. It should drop off the spatula in large thick flakes, take considerable time to set, and the surface should not be glossy.

When this mottling condition has been obtained, the colouring matter, which would be ultramarine for the blue mottled and manganese dioxide for the grey mottled soap (3-4 lb. ultramarine or 1-3 lb. manganese dioxide being sufficient for 1 ton of soap), is mixed with a little water and added to the boiling soap—the boiling is continued until all is thoroughly amalgamated, and when the steam is shut off the contents of the pan are ready for cleansing.

Mottled soap is run into wooden frames, which, when full, are covered over and allowed to cool very gradually. On cooling slowly, large crystals are produced which result in a distinct bold mottle; if the cooling is too rapid, a small crystal is obtained and the mottle is not distributed, resulting in either a small mottle, or no mottle at all, and merely a general coloration. In fact, the entire art of mottling soap consists in properly balancing the saline solutions and colouring matter, so that the latter is properly distributed throughout the soap, and does not either separate in coloured masses at the bottom of the frame, or uniformly colour the whole mass.

A sample of the soap should test 45 per cent. fatty acids, and the amount of salt would range from 1/2 to 1 per cent.

Some of the English mottled soaps, especially those made from materials which give a yellow-coloured ground, are bleached by soaking in brine, or pickling in brine containing 2 per cent. of bleach liquor. The resultant soap has a white ground and is firm. The bleach liquor may be made by mixing 1 cwt. bleaching powder with 10 cwts. of soda ash solution (15 deg. Tw., 10 deg. B.), allowing to settle, and using the clear liquid, or by mixing 2 parts soda ash solution with 1 part of bleaching powder solution, both solutions being 30 deg. Tw. (18.8 deg. B.).

Milling-base.—The materials generally used are tallows and cocoa-nut oils of the finest quality. The tallow is thoroughly saponified first, and the graining is performed by the aid of caustic soda lye in preference to salt. The half-spent lyes are withdrawn, and the cocoa-nut oil added to the pan. This is saponified, and when the saponification is complete, "boiling-on-strength" is proceeded with. Special care should be devoted to the "boiling-on-strength" operation—its value in good soap-making cannot be over-rated—and perfect saponification must be ensured. The half-spent lyes are allowed to deposit during the night, and the soap must be carefully examined next morning to ascertain if any alkali has been absorbed. If the caustic taste is permanent the strengthening operation is complete, but should any caustic have been absorbed, further addition of alkali must be made and the boiling continued. These remarks apply equally to all soaps.

The soap, when ready, is fitted.

Bleached palm oil, olive oil, castor oil and lard are also employed in the production of special milling soap bases, a palm oil soap being specially suitable for the production of a violet-scented toilet soap.

Yellow Household Soaps. (a) Bar Soaps.—These are made from tallow with an admixture of from 15-25 per cent. rosin. The best quality is known in the South and West of England as Primrose Soap, but is designated in the North of England by such names as Golden Pale, Imperial Pale, Gold Medal Pale, etc. Tallow alone produces a very hard soap of inferior lathering qualities; but rosin combines with alkali to form a soft body, which, although not a soap in the strict sense of the term, is readily soluble in water, and in admixture with the durable tallow soap renders it more soluble in water and thereby increases its lathering properties.

The rosin may be added to the soap-pan after a previous partial saponification with soda ash, and removal of colouring matter, and finally saponified with caustic soda lye, or, as is more generally adopted, as a rosin change. The pan is opened with caustic soda lye and saturation of the rosin takes place rapidly; when completely saponified it is grained with salt, and the coloured lye allowed to deposit and finally withdrawn.

The four operations already detailed apply to this soap.

Cheaper pale soaps may be made from lower grades of tallow and rosin and are generally silicated.

(b) Tablet or Washer Type.—A demand has arisen for soap of free lathering qualities, which has become very popular for general household use. This soap is usually made from a mixture of cotton-seed oil, tallow, and cocoa-nut oil, with a varying amount of rosin. The tallow yields firmness and durability whilst the other constituents all assist in the more ready production of a copious lather.

As to what amount of rosin can be used to yield a finished soap of sufficient body and satisfactory colour, this naturally depends upon the grade of raw material at the soap-makers' disposal. Those fats and oils which yield firm soaps, will, of course, allow a greater proportion of rosin to be incorporated with them than materials producing soaps of less body. Rosin imparts softness to a soap, and also colour.

This is a fitted soap and full details of manufacture have already been given.

Cheaper soaps are produced from lower grade materials hardened with alkaline solutions.

Resting of Pans and Settling of Soap.—The fitted soap is allowed to settle from four to six days. The period allowed for resting is influenced, however, not only by the size of the boil, and the season, but also by the composition of the soap, for if the base has been made from firm stock it is liable to cool quicker than a soap produced from soft-bodied materials.

On subsidence, the contents of the pan will have divided into the following:—

First. On top, a thin crust of soap, with perhaps a little light coloured fob, which is returned to the pan after the removal of the good soap.

Second. The good settled soap, testing 62-63 per cent. fatty acids. The subject of removing and treatment of this layer is fully dealt with in the next chapter.

Third. A layer of darker weak soap, termed "nigre," which on an average tests 33 per cent. fatty acids, and, according to the particular fit employed, will amount to from 15-20 per cent. of the total quantity of soap in the pan.

The quantity of nigre may vary not only with the amount of water added during finishing, but is also influenced by the amount of caustic alkali remaining in the soap paste prior to fitting. If the free caustic alkali-content is high, the soap will require a large amount of water to attain the desired fit. This water renders the caustic into a lye sufficiently weak to dissolve a quantity of soap, consequently, as the "nigre" is a weak solution of soap together with any excess of alkali (caustic or carbonate) and salt which gravitates during the settling, the quantity is increased.

Fourth. A solution containing alkaline salts, mostly carbonates and chlorides, with a little caustic.

The amount of the layer is very variable, and doubtless, under certain physical conditions, this liquor has separated from the nigre.

Utilisation of Nigres.—The nigres are boiled and the liquor separated by graining with salt. Nigre may be utilised in various ways.

(1) It may be used several times with new materials. This particularly refers to soaps of the "Washer" type. The colour of the nigre will determine the number of times it can be employed.

(2) It may be incorporated with a soap of a lower grade than the one from which it was obtained. In this case a system is generally adopted; for example, soap of the best quality is made in a clean pan, the nigre remaining is worked up with fresh material for soap of the next quality, the nigre from that boil, in its turn, is admixed with a charge to produce a batch of third quality, and the deposited nigre from this is again used for a fourth quality soap—the nigre obtained from this latter boil would probably be transferred into the cheapened "washer" or perhaps if it was dark in colour into the brown soap-pan.

(3) The nigre may be fitted and produce a soap similar to the original soap from which it was deposited. It is advisable to saponify a little fat with it.

(4) Nigres from several boils of the same kind of soap can be collected, boiled, and fitted. The settled portion may be incorporated with a new charging to keep the resultant soap uniform in colour—unless this is done, the difference in colour between boils from new materials alone, and those containing nigre, is very noticeable. The nigre settled from this fitted nigre boil would be utilised in brown soap.

(5) According to its colour, and consistence, a nigre may be suitable for the production of disinfectant, or cold-water soaps.

(6) Nigre may be bleached by treatment with a 20 per cent. solution of stannous chloride—1 cwt. of this solution (previously heated) is sufficient to bleach 20 tons of nigre.

Transparent Soaps.—The production of transparent soaps has recently been fully studied, from a theoretical point of view, by Richardson (J. Amer. Chem. Soc., 1908, pp. 414-20), who concludes that the function of substances inducing transparency, is to produce a jelly and retard crystallisation.

The old-fashioned transparent soap is prepared by dissolving, previously dried, genuine yellow soap in alcohol, and allowing the insoluble saline impurities to be deposited and removed. The alcoholic soap solution is then placed in a distillation apparatus, or the pan containing the solution is attached by means of a still head to a condenser, and the alcohol distilled, condensed and regained. The remaining liquid soap, which may be coloured and perfumed, is run into frames and allowed to solidify.

The resultant mass is somewhat turbid, but after storage in a room at 95 deg. F. (35 deg. C.) for several months, becomes transparent.

The formation of the transparency is sometimes assisted and hastened by the addition of glycerine or a solution of cane-sugar.

A patent has been granted to A. Ruch (Fr. Pat. 327,293, 1902) for the manufacture of transparent glycerine soap by heating in a closed vessel fatty acids together with the requisite quantity of alcoholic caustic soda solution necessary for saponification, and cooling the resultant soap. It is also proposed to add sugar solution.

Cheaper qualities of transparent soaps are made by the cold process with or without the aid of alcohol and castor oil, and with the assistance of glycerine or cane-sugar.

With the continual demand for cheaper production, sugar solution has gradually, in conjunction with castor oil, which produces transparency, superseded the use of alcohol and glycerine.

For a small batch, 56 lb. Cochin cocoa-nut oil and 56 lb. sweet edible tallow may be taken, melted at 130 deg. F. (54 deg. C.), and carefully strained into a small steam-jacketed pan. It is imperative that the materials should be of the highest quality and perfectly clean. Twenty-three lb. of pure glycerine and 56 lb. of bright caustic soda solution made from high grade caustic and having a density of 72 deg. Tw. (38 deg. B.) are crutched into the fat; the alcohol, which would be 45 lb. in this example, is then added. The whole must be most intimately incorporated, and the pan covered and allowed to rest for one hour or one and a half hours. Saponification should ensue.

To produce a transparent glycerine soap with the aid of castor oil, and with or without the use of alcohol, the following is the procedure:—

Cochin cocoa-nut oil, sweet edible tallow, and castor oil, of each 56 lb. are taken, warmed to 130 deg. F. (54 deg. C.), and carefully strained into the jacketed pan. If it is desired to use glycerine and cane sugar solution, and no alcohol, the glycerine (25 lb.) is now stirred into the fats together with the requisite (83 lb.) caustic soda solution 72 deg. Tw. (38 deg. B.). If it is intended to use alcohol and sugar, and no glycerine, the latter is replaced by 47 lb. of alcohol, and added after the incorporation of the caustic soda lye.

The whole being thoroughly crutched, the pan is covered and saponification allowed to proceed for one hour or one and a half hours. Should the saponification for some reason be retarded, a little steam may be very cautiously admitted to the jacket of the pan, the mass well crutched until the reaction commences, and the whole allowed to rest the specified time.

Whilst saponification is proceeding, the "sugar solution" is prepared by dissolving 50 lb. cane sugar in 50 lb. water, at 168 deg. F. (76 deg. C.), to which may be added 5 lb. soda crystals, and any necessary colouring matter. The water used for this solution should be as soft as possible, as hard water is liable to produce opaque streaks of lime soap.

It is absolutely necessary before proceeding further to ensure that saponification is complete. A greasy, soft feel and the presence of "strength" (caustic) would denote incomplete saponification—this can only be remedied by further heating and crutching. Deficiency of caustic alkali should also be avoided, and, if more lye is required, great care must be exercised in its addition.

Saponification being completed, the sugar solution is carefully and gradually crutched into the soap; when the contents of the pan have become a homogeneous and syrupy mass, the crutching is discontinued, and the pan is covered for one hour. The heat of the soap in the pan should not exceed 170 deg. F. (77 deg. C.).

Having rested the necessary period, the soap will have a slight froth on the surface, but will be clear underneath and appear dark. Samples may now be withdrawn, cooled, and examined prior to framing. If the process has been successfully performed the soap will be firm and transparent, of uniform colour, and possess only a faintly alkaline taste.

If the sample be firm but opaque, more sugar solution is required; this should be added very carefully whilst crutching, an excess being specially guarded against. If the sample be soft, although transparent, and the alkaline taste not too pronounced, the soap evidently contains an excess of water, which may be remedied by the addition of a small quantity of soda ash; too much soda ash (carbonates) must be avoided, lest it should produce efflorescence.

Having examined the soap and found it to be correct, or having remedied its defects, the soap in the pan is allowed to cool to 145 deg. F. (63 deg. C.) and perfume added. The soap is now quickly filled into narrow frames and allowed to cool rapidly.

The blocks of soap should not be stripped until quite cold throughout, and they should be allowed to stand open for a while before slabbing. When freshly cut into tablets, the soap may appear somewhat turbid, but the brightness comes with the exposure it will receive prior to stamping and wrapping.

Saponifying Mineral Oil.—This sounds somewhat incongruous, as mineral oil is entirely unsaponifiable. Most of the suggestions for this purpose consist of the incorporation of mineral oil, or mineral oil emulsified by aid of Quillaia bark, with a cocoa-nut oil soap, and in all these instances the hydrocarbon merely exists in suspension.

G. Reale (Fr. Pat. 321,510, 1902), however, proposes to heat mineral oil together with spermaceti and strong alkali, and states that he transforms the hydrocarbons into alcohols, and these, absorbing oxygen, become fatty acids, which are converted into soap by means of the alkali.

In this connection may be quoted the interesting work of Zelinsky (Russ. Phys. Chem. Ges. Zeits. Angew. Chem., 1903, 37). He obtained substances, by acting with carbon dioxide upon magnesia compounds of chlorinated fractions of petroleum, which when decomposed by dilute sulphuric acid, yielded various organic acids. One of these acids on heating with glycerine formed tri-octin, which had the properties of a fat.

Dr. Engler, in confirmation of the theory of the animal origin of some petroleums, obtained what might be described as petroleum (for it contained almost all the hydrocarbons present in the natural mineral oil) by distilling animal fats and oils under pressure.

Electrical Production of Soap.—Attempts have been made to produce soap electrically by Messrs. Nodon, Brettonneau and Shee (Eng. Pat. 22,129, 1897), and also by Messrs. Merry and Noble (Eng. Pat. 2,372, 1900).

In the former patent, a mixture of soda-lye and fat is agitated by electricity at a temperature of 194 deg.-212 deg. F. (90 deg.-100 deg. C.), while in the latter caustic alkali is electrolytically produced from brine, and deposited on wire-netting in the presence of fat, which is thereby saponified.



CHAPTER VI.

TREATMENT OF SETTLED SOAP.

Cleansing—Crutching—Liquoring of Soaps—Filling—Neutralising, Colouring and Perfuming—Disinfectant Soaps—Framing—Slabbing—Barring—Open and Close Piling—Drying—Stamping—Cooling.

Cleansing.—After completion of saponification, and allowing the contents of the pan to settle into the various layers, as described in the preceding chapter, the actual soap, forming the second layer, is now transferred to the frames, this being generally termed "cleansing" the soap. The thin crust or layer at the top of the pan is gently removed, and the soap may be either ladled out and conveyed to the frames, or withdrawn by the aid of a pump from above the nigre through a skimmer (Fig. 1), and pipe, attached by means of a swivel joint (Fig. 2) (which allows the skimmer pipe to be raised or lowered at will by means of a winch, Fig. 3), to a pipe fitted in the side of the pan as fully shown in Fig. 4, or the removal may be performed by gravitation through some mechanical device from the side of the copper.



Every precaution is taken to avoid the presence of nigre in the soap being cleansed.



The temperature at which soap may be cleansed depends on the particular grade—soaps requiring to be liquored should not be cleansed too hot or a separation will take place, 150 deg. F. (66 deg. C.) may be taken as a suitable temperature for this class of soap; in the case of firm soaps, such as milling base, where cooling is liable to take place in the pan (and thus affect the yield), the temperature may be 165 deg.-170 deg. F. (74 deg.-77 deg. C.). This latter class of soap is generally run direct to the frames and crutched by hand, or, to save manual labour, it may be run into a power-driven crutching pan (neutralising material being added if necessary) and stirred a few times before framing.



Crutching.—This consists of stirring the hot soap in the frames by hand crutches (Fig. 5) until the temperature is sufficiently lowered and the soap begins to assume a "ropiness". Crutching may also be performed mechanically. There are various types of mechanical crutchers, stationary and travelling. They may be cylindrical pans, jacketed or otherwise, in the centre of which is rotated an agitator, consisting of a vertical or horizontal shaft carrying several blades (Fig. 6) or the agitator may take the form of an Archimedean screw working in a cylinder (Fig. 7).



The kind of soap to be crutched, whether thin or stiff, will determine the most suitable type for the purpose. The former class includes "washer" soap which is generally neutralised, and coloured and perfumed, if necessary, in these crutching pans, and in that case they are merely used for mixing the liquids with the hot soap prior to its passage along wooden spouts (Fig. 8) provided with outlets over the frames, in which the crutching is continued by hand. In the case of stiff soaps requiring complete incorporation of liquor, the screw type is preferable, the soap being forced upwards by the screw, and descending between the cylinder and the sides of the pan, while the reverse action can also be brought into play. The completion of crutching is indicated by the smoothness and stiffness of the soap when moved with a trowel, and a portion taken out at this point and cooled should present a rounded appearance. When well mixed the resultant product is emptied directly into wheel-frames placed underneath the outlet of the pan. It is important that the blades or worm of the agitating gear be covered with soap to avoid the occlusion of air and to prevent the soap becoming soft and spongy.



Liquoring of Soaps.—This consists of the addition of various alkaline solutions to soap to produce different qualities, and is best performed in the crutching machines, although it is in some instances carried out in the frames. In the history of soap-making a large number and variety of substances have been suggested for the purpose of accomplishing some real or supposed desirable effect when added to soap. Many of these have had only a very short existence, and others have gradually fallen out of use.

Amongst the more practical additions most frequently adopted may be mentioned carbonate of soda, silicate of soda, and pearl ash (impure carbonate of potash). The carbonate of soda may be used in the form of "soda crystals," which, containing 62.9 per cent. of water, dissolves in its own water of crystallisation on heating, and is in that manner added to the hot soap. In the case of weak-bodied soap, this addition gives firmness and tends to increase the detergent qualities.

The soda carbonate may also be added to soap as a solution of soda ash (58 deg. alkali) either concentrated, 62 deg. Tw. (34 deg. B.), or of various strengths from 25 deg. Tw. (16 deg. B.) upwards. This solution stiffens and hardens soap, and the addition, which must not be excessive, or efflorescence will occur, is generally made at a temperature of 140 deg. F. (60 deg. C.). Care should always be taken in the choice of solutions for liquoring. Strong soda ash solution with a firm soap will result in a brittle product, whereas the texture of a weak soap would be greatly improved by such addition.

A slight addition of a weak solution of pearl ash, 4 deg.-8 deg. Tw. (2.7-5.4 deg. B.), improves the appearance of many soaps intended for household purposes.

For yellow soaps, containing a low percentage of fatty acids, solutions of silicate of soda of varying strengths are generally used.

It is always advisable to have a test sample made with the soap to ascertain what proportion and what strength of sodium silicate solution is best suited for the grade of soap it is desired to produce. It is important that the soap to be "silicated" should be distinctly alkaline (i.e., have a distinct caustic taste), or the resultant soap is liable to become like stone with age. The alkaline silicate of soda (140 deg. Tw., 59.5 deg. B.) is the quality most convenient for yellow soaps; this may be diluted to the desired gravity by boiling with water. For a reduction of 3-4 per cent. fatty acids content, a solution of 6 deg. Tw. (4 deg. B.) (boiling) is most suitable, and if the reduction desired is greater, the density of the silicate solution should be increased; for example, to effect a reduction of 20 per cent. fatty acids content, a solution of 18 deg. Tw. (12 deg. B.) (boiling) would probably be found to answer.

In some instances 140 deg. Tw. (59.5 deg. B.) silicate may be added; experiment alone will demonstrate the amount which can be satisfactorily incorporated without the soap becoming "open," but 1/10 of the quantity of soap taken is practically a limit, and it will be found that the temperature should be low; the same quantity of silicate at different temperatures does not produce the same result. Various other strengths of sodium silicate are employed, depending upon the composition and body of the soap base—neutral silicate 75 deg. Tw. (39.4 deg. B.) also finds favour with some soap-makers. Mixtures of soda crystals or soda ash solution with silicate of soda solution are used for a certain grade of soap, which is crutched until smooth and stiff. Glauber's salt (sodium sulphate) produces a good smooth surface when added to soap, but, owing to its tendency to effloresce more quickly than soda carbonate, it is not so much used as formerly.

Common salt sometimes forms an ingredient in liquoring mixtures. Potassium chloride and potassium silicate find a limited use for intermixing with soft soaps.

It will be readily understood that hard and fast rules cannot be laid down for "liquoring" soap, and the correct solution to be employed can only be ascertained by experiment and experience, but the above suggestions will prove useful as a guide towards good results. A smooth, firm soap of clear, bright, glossy appearance is what should be aimed at.

Filling.—Some low-grade soaps contain filling, which serves no useful purpose beyond the addition of weight. Talc is the most frequently used article of this description. It consists of hydrated silicate of magnesium and, when finely ground, is white and greasy to the touch. The addition of this substance to the hot soap is made by suspending it in silicate of soda solution.

Whatever filling material is used, it is important that the appearance of the soap should not be materially altered.

Neutralising, Colouring and Perfuming.—The free caustic alkali in soap, intended for toilet or laundry purposes, is usually neutralised during the cleansing, although some soap manufacturers prefer to accomplish this during the milling operation. Various materials have been recommended for the purpose, those in most general use being sodium bicarbonate, boric acid, cocoa-nut oil, stearic acid, and oleic acid.

The best method is the addition of an exact quantity of sodium bicarbonate (acid sodium carbonate), which converts the caustic alkali into carbonate. The reaction may be expressed by the equation:—

NaOH + NaHCO{3} = Na{2}CO{3} + H{2}O Caustic soda Bicarbonate of soda Carbonate of soda Water

Boric acid in aqueous or glycerine solutions, and borax (biborate of soda) are sometimes used, but care is necessary in employing these substances, as any excess is liable to decompose the soap.

The addition of cocoa-nut oil is unsatisfactory, the great objection being that complete saponification is difficult to ensure, and, further, there is always the liability of rancidity developing. Stearic and oleic acids are more suitable for the purpose, but oleic acid has the disadvantage that oleates are very liable to go rancid.

A large number of other substances have been proposed, and in many instances patented, for neutralising the free caustic alkali. Among these may be mentioned—Alder Wright's method of using an ammoniacal salt, the acid radicle of which neutralises the caustic alkali, ammonia being liberated; the use of sodium and potassium bibasic phosphate (Eng. Pat. 25,357, 1899); a substance formed by treating albumen with formalin (Eng. Pat., 8,582, 1900); wheat glutenin "albuminoses" (albumen after acid or alkaline treatment); malt extract; and egg, milk, or vegetable albumen.

The colouring matter used may be of either vegetable or coal-tar origin, and is dissolved in the most suitable medium (lye, water, or fat). The older types of colouring matter—such as cadmium yellow, ochres, vermilion, umbers—have been superseded.

In the production of washer household soaps, a small quantity of perfume is sometimes added.

Disinfectant Soaps.—To the soap base, which must be strong to taste, is added from 3 to 4 per cent. of coal-tar derivatives, such as carbolic acid, cresylic acid, creosote, naphthalene, or compounds containing carbolic acid and its homologues. The incorporation is made in the crutching pan, and further crutching may be given by hand in the frames.

Framing.—The object of framing is to allow the soap to solidify into blocks. The frames intended for mottled soaps, which require slow cooling, are constructed of wood, often with a well in the base to allow excess of lye to accumulate—for other soaps, iron frames are in general use. The frame manufactured by H. D. Morgan of Liverpool is shown in Fig. 9.

As soon as the frame is filled, or as soon as the crutching in the frame is finished, the soap is smoothed by means of a trowel, leaving in the centre a heap which slopes towards the sides. Next day the top of the soap is straightened or flattened with a wooden mallet, this treatment assisting in the consolidation.



The length of time the soap should remain in frames is dependent on the quality, quantity, and season or temperature, and varies usually from three to seven days. When the requisite period has elapsed, the sides and ends of the frames are removed, and there remains a solid block of soap weighing from 10 to 15 cwt. according to the size of frame used. The blocks, after scraping and trimming, are ready for cutting into slabs.