The presence of these salts in water form insoluble lime soaps which act as inert bodies as far as their value for the common use of soap is concerned. Where the percentage of lime in water is large this should be removed. A method generally used is to add about 5% of 20° B. sodium silicate to the hard water. This precipitates the lime and the water is then sufficiently pure to use.
Salt, known as sodium chloride, is used to a large extent in soap making for "salting out" the soap during saponification, as well as graining soaps. Soap ordinarily soluble in water is insoluble in a salt solution, use of which is made by adding salt to the soap which goes into solution and throws any soap dissolved in the lyes out of solution. Salt may contain magnesium and calcium chlorides, which of course are undesirable in large amounts. The products on the market, however, are satisfactory, thus no detail is necessary.
Filling materials used are sodium silicate, or water glass, talc, silex, pumice, starch, borax, tripoli, etc.
Besides these other materials are used in the refining of the oils and fats, and glycerine recovery, such as Fuller's earth, bichromates of soda or potash, sulphate of alumina, sulphuric and hydrochloric acids and alcohol.
A lengthy description of these substances is not given, as their modes of use are detailed elsewhere.
FOOTNOTES:
[1] Seifensieder Zeit, 1913, 40, p. 687, 724, 740.
[2] Official Methods, see Bull. 107, A. O. A. C., U. S. Dept. Agricult.
[3] Journ. Coll. of Engin. Tokyo Imper. Univ. (1906), p. 1. Abs. Chem. Revue f. d. Fett-u. Harz, Ind. 16, p. 84; 20, p. 8.
[4] Meyerheim—Fort. der Chem., Physik. und Physik. Chem. (1913), 8. 6, p. 293-307.