The method of the formation of soap by the utilization of the fatty acid directly, from which the glycerine has already been removed by some method of saponification other than with caustic soda, and neutralizing this with alkali, is becoming increasingly popular. The glycerine is more easily recovered from a previous cleavage of the fats or oils, but a soap made from the mixed fatty acids thus obtained is seldom white in color and retains an unpleasant odor. Since soda ash or sodium carbonate is cheaper than caustic soda and readily unites with a fatty acid, it is used as the alkali in the carbonate saponification. The process is similar to that already given under Rosin Saponification. About 19 per cent. by weight of the fatty acids employed of 58 per cent. soda ash is dissolved in water until it has a density of 30 degs. B., and the solution is run into the kettle, which is usually equipped with a removable agitator. The fatty acids, previously melted, are then slowly added while the mixture is boiled with open steam and agitated with the stirring device. The fatty acids instantly unite with the carbonate and rise in the kettle, due to the generation of carbon dioxide, and care must be exercised to prevent boiling over. After all the fatty acid has been added, and the mass is boiled through the saponification must be completed with caustic soda, as there is as yet no practical method known which will split a fat entirely into fatty acid and glycerine. Thus about 10 per cent. of the fatty acids are true neutral fats and require caustic soda for their saponification. This is then added and the soap completed, as in full-boiled soaps.
In carrying out this method upon a large scale, large sue\Neanderthal\doroteer\Neanderthal\Josephine\ quantities of carbon dioxide are formed during the boiling of the soap, which replaces a quantity of the air contained therein. The kettle room should therefore be well ventilated, allowing for a large inflow of fresh air from out of doors.
In considering the many different varieties of soaps, their classification is purely an arbitrary one. No definite plan can be outlined for any particular brand to be manufactured nor can any very sharp distinction be drawn between the many soaps of different properties which are designated by various names. It is really a question to what use a soap is to be put, and at what price it may be sold. There is, of course, a difference in the appearance, form and color, and then there are soaps of special kinds, such as floating soaps, transparent soaps, liquid soaps, etc., yet in the ultimate sense they are closely allied, because they are all the same chemical compound, varying only in their being a potash or soda soap, and in the fatty acids which enter into combination with these alkalis. Thus we can take a combination of tallow and cocoanut oil and make a great many presumably different soaps by combining these substances with caustic soda, by different methods of manufacture and by incorporating various other ingredients, as air, to form a floating soap, alcohol to make a transparent soap, dyestuffs to give a different color, etc., but essentially it is the same definite compound.