To carry out this process the following formulae have been found by experience to give satisfactory results.
Tallow 100 Rosin 60 Silicate of Soda 25 Soda Lye, 36° B. 85
Tallow 100 Rosin 100 Lye, 36° B. 105 Silicate of Soda 25 Sal Soda Solution 20
In any of these formulas the sodium silicate (40° B.) may be increased to the same proportion as the fats used. By so doing, however, twenty pounds of 36° B. lye must be added for every hundred pounds of silicate additional to that indicated or in other words, for every pound of silicate added 20 per cent. by weight of 36° B. lye must be put into the mixture. The rosin may also be replaced by a previously made rosin soap.
To make a semi-boiled soap, using any of the above formulae, first melt the rosin with all or part of the fat, as rosin when melted alone readily decomposes. When the mixture is at 150° F. run it into the crutcher and add the lye. Turn on sufficient dry steam to keep the temperature of the soap at about 150° F. in the winter or 130° F. in summer. After the mass has been mixed for half an hour, by continuously crutching the soap it will at first thicken, then grain and it may again become thick before it becomes smooth. When the mass is perfectly smooth and homogeneous drop into a frame and crutch in the frame by hand to prevent streaking. After standing the required length of time the soap is finished into cakes as usual.
Settled rosin soaps are made from tallow, grease, cottonseed oil, bleached palm oils of the lower grades, corn oil, soya bean oil, arachis oil, distilled garbage grease, cottonseed foots or fatty acids together with an addition of rosin, varying from 24 per cent. to 60 per cent. of the fatty acids which should titer from 28 to 35. A titer lower than 28 will prevent the finished kettle of soap from being capable of later taking up the filling materials. As has already been stated under hardened oils, these being very much higher in titer allow a greater percentage of rosin to be added. Thus hardened fish oils and cottonseed oil are gradually being more extensively employed in soaps of this character.
The procedure of handling the kettle is similar to that given under full boiled soap. The stock is steamed out into a settling tank and allowed to settle over night, after which it is pumped into the soap kettle. Having stocked the kettle, open steam is turned on and 10°-12° B. lye is run in, while using a steam pressure of ninety to one hundred pounds in order to prevent too great a quantity of condensation of the steam, the water thus being formed weakening the lye. If a steam pressure of fifty to sixty pounds is available, a stronger lye (20° B.) should be added. Care must be taken not to allow the lye to flow in too rapidly or the soap will not grain. The saponification is only attained by prolonged boiling with sufficient lye of proper strength. When saponification has taken place, the mass begins to clear and a sample taken out with a paddle and cooled should show a slight pink with a 1 per cent. alcoholic phenolphthalein solution.