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 quant.i.ty 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 a.s.sistance 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for cheaper production, sugar solution has gradually, in conjunction with castor oil, which produces transparency, superseded the use of alcohol and glycerine.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 F. (54 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 Tw. (38 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 F. (54 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 Tw.

(38 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 r.e.t.a.r.ded, a little steam may be very cautiously admitted to the jacket of the pan, the ma.s.s 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 F. (76 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 h.o.m.ogeneous and syrupy ma.s.s, the crutching is discontinued, and the pan is covered for one hour. The heat of the soap in the pan should not exceed 170 F. (77 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 p.r.o.nounced, the soap evidently contains an excess of water, which may be remedied by the addition of a small quant.i.ty 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 F. (63 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 n.o.ble (Eng. Pat. 2,372, 1900).

In the former patent, a mixture of soda-lye and fat is agitated by electricity at a temperature of 194-212 F. (90-100 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.

[Ill.u.s.tration: FIG. 1.--Skimmer, with f.l.a.n.g.e for attachment to skimmer-pipe.]

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

[Ill.u.s.tration: FIG. 2.--Swivel-joint.]

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 F. (66 C.) may be taken as a suitable temperature for this cla.s.s 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 165-170 F.

(74-77 C.). This latter cla.s.s 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.

[Ill.u.s.tration: FIG. 3.--Winch.]

[Ill.u.s.tration: FIG. 4.--Soap-boiling pan, showing skimmer pipe, swivel and winch.]

[Ill.u.s.tration: FIG. 5.--Hand crutch.]

[Ill.u.s.tration: FIG. 6.--Mechanical crutcher.]

_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 a.s.sume 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).

[Ill.u.s.tration: FIG. 7.--Mechanical crutcher.]

The kind of soap to be crutched, whether thin or stiff, will determine the most suitable type for the purpose. The former cla.s.s 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 pa.s.sage 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.

[Ill.u.s.tration: FIG. 8.--Wooden soap spout.]

_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 alkali) either concentrated, 62 Tw. (34 B.), or of various strengths from 25 Tw. (16 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 F.

(60 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, 4-8 Tw. (2.7-5.4 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 Tw., 59.5 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 Tw. (4 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 Tw. (12 B.) (boiling) would probably be found to answer.

In some instances 140 Tw. (59.5 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 quant.i.ty of soap taken is practically a limit, and it will be found that the temperature should be low; the same quant.i.ty 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 Tw. (39.4 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.