According to the Soapmaker and Perfumer, the chief fat used in the manufacture of either smoothed or grained soft soap is linseed oil, and this, if pure and good, gives a lasting, line transparent soap, and allows more rilling than any other fat. Properly made, linseed-oil soaps stand cold the best of any, and even if they have become somewhat turbid during exceptionally sharp weather, they recover their appearance as soon as it gets warmer. The seed yields from 20 to 30 per cent, of the oil by pressure, and the oil will keep a long time without becoming rancid or deteriorating in any way. Besides linseed oil, cottonseed and earthnut oil are much used in soft soap manufacture, and for the cheapest and most filled kinds, oil sediments full of stearine are often employed. These answer in the summer, but are apt to cause trouble by efflorescing in cold weather. Linseed-oil soft soaps are principally used for household purposes, and are of many varieties. Unfilled natural-grain soft soap is the best, and is prepared from two parts of pale linseed oil and one part of good tallow. If the evaporation is carried on till nearly all the froth has disappeared, the soap will be more durable, and faster graining than if the action is pushed farther.

For technical purposes oleine gives better results than linseed oil, and produces more soap, weight for weight, but the oleine must not have ixndergoue decomposition. Distilled oleine is often found to have been partially decomposed in the distillation. For some purposes, too, tallow-oleine grain soap is not soluble enough. In washing fleeces, for instance, the hard grain soap often lodges undissolved in the wool, especially if old soap has been used. This is a waste of soap, and hinders the subsequent dyeing operations. For such use, the soap is best made from oleine alone; or a hard potash soap with plenty of carbonate in it may be used. Good soaps for the purpose can also be got from mixtures of oleine with its own weight of palm oil, but if these soaps are kept too long in stock they lose in solubility. A good recipe for a natural-grain textile soap is oleine, 51b.; cottonseed oil, 4 1/2 lb.; hard fat, 61b.; bleached palm oil, 4 1/2 lb.; and raw palm oil, 2 lb. A few pounds of tallow not containing too much stearine can also be worked in, and the hard fat mentioned can be replaced by bleached palm oil. Good Lagos oil gives a fine round grain. Such soaps can be tilled easily to some extent, and in winter best with 15° B. potash, in summer with 13s B. potassium chloride.

It is most important to attend to the composition of the lye. In using 50 B. potash lye, it should, in the colder season of the year, be mixed with a quarter of its weight of 97 to 98 per cent, carbonate of potash in solution, so as to make a 25 B. lye. As with all natural-grain soaps, these soft soaps must be got as nearly neutral as possible. If this and the evaporation are properly seen to, the soap will dissolve easily and the grain will not be too solid. The washing power of a soap depends upon its solubility and lathering power. As potash soaps containing resin are the most soluble, the latter substance increases the cleansing power. Most soft soaps, too, contain an excess of alkali, especially those filled with meal, and this alkali still further increases the washing capabilities of the soap. Linseed-oil soft soaps are made quite unfilled, or containing a high percentage of filling. To get the soap as transparent and as light in colour as possible, even the palest oil sometimes is bleached, and in summer cottonseed oil is used with it. The bleaching is usually done with a 30: B. potash lye not too caustic.

When a strong lye is used, the dark precipitate which contains the colouring matter, and also the product of the saponification of the free fatty acid originally present, can be utilised in manufacturing low-grade soaps. One hundred pounds of linseed oil can be bleached with 61b. to 71b. of the above lye, the lye being run whilst warm into the oil in a thin stream, and being well crutched into it for half an hour. By crunching is meant the stirring together of the ingredients by means of a perforated piece of wood or iron attached to a pole. If the oil is very pale, 5 lb. of lye will suffice for the bleaching; but in any case bleached oil wants a stronger lye for saponification than unbleached. With the latter the lye should not contain much carbonate, and should not exceed 18o B. in strength. Later, stronger lye is added to prevent the soap getting too thick. For the saponification of 100 lb. of oils, 150 lb. of 25' B. potash lye are used generally. To 100 lb. of oil in a pan, 25 lb. of 20; B. lye and 10 lb. of water are added. To ensure quicker union, about 5 lb. of resin should also be added. Heat all up and crutch repeatedly; when an emulsion is formed, boil it in the pan. Now gradually add the rest of the lye, boiling up after each addition.

Finally, evaporate over not too strong a fire. In winter it is better not to use soda lye, but in summer soda to the amount of 30 per cent, of the fat can replace part of the potash. The soda is put in all together, after about one-third of the potash lye is in the pan. The resin is often added at the end. and if the soap is rather alkaline, usually makes it about right. A well-finished soap must be thick in the sample glass, should show a good flower, and be quite clear when cold. When soda is used, less evaporation is needed. Summer soft soaps must not show so much flower as a winter-made soap, and should keep better. There may be rather more carbonate in the lye if the soap is not to be filled, and carbonate of potash can be added. The above process gives a very pale amber soap. For filling, the best substance is 13° B. solution of potassium chloride, which is crutched in when the finished soap has partly cooled. In adjusting or fitting a soft soap, the use of carbonated alkali is essential. All soft soaps boil tough before they are properly adjusted. When right they break off rather short from the spatula. A piece as big as a half-crown should be set at the edges, but should yield liquid soap on pressure with the finger in the middle.

Subsequent filling will not do away with the bad results of careless fitting, and in any case the soap will turn rancid if deficient in alkali, and brittle and unsatisfactory if there is too much. The following is a good recipe for a well-filled soap. Linseed oil, 100 lb.; resin, 20 lb.; meal, 521b.; potash (15J B.), 581b.; potassium chloride (23° B.), 201b.: and waterglass, 151b. Besides this, the addition of from 561b. to 581b. of fitting lye of 30° B. will be made necessary by the filling. It is often asserted that more filling is wanted in summer than in winter. This is only correct when soda lye is not used. With filled soaps, excess of lye is to be particularly avoided. If the soap is to be made grain, very fine indigo is ground to the finest possible powder, boiled in weak lye, and added to the pan at the very last, when the soap is just going off the boil. The colour is better and more uniform if the indigo is ground up with its own weight of fuming sulphuric acid, and then left to stand for several days in a warm place. The solution is then stirred up with soda crystals until fairly neutralised. In this way the colour is made very soluble in the soap, and is crutched into it very easily, giving an even-coloured product.

About 1 oz. of indigo is used for every 631b. of soap. Formerly hemp oil was used always for green soft soaps. This oil resembles linseed in its properties, but has a fine green colour. It gives a good leaf-green soap, but the high price of hemp oil precludes its extensive employment.