Soap-Making Manual / A Practical Handbook on the Raw Materials, Their Manipulation, Analysis and Control in the Modern Soap Plant.

by Edgar George Thomssen

SILICA AND SILICATES.

The insoluble silicates, sand, etc., are present in the ignited residue in the determination of insoluble matter. Sodium silicate, extensively used as a filler, however, will only show itself in forming a pasty liquid. Where it is desired to determine sodium silicate, 10 grams of soap are ashed by ignition, hydrochloric acid added to the ash in excess and evaporated to dryness. More hydrochloric acid is then added and the mass is again evaporated until dry; then cooled; moistened with hydrochloric acid; dissolved in water; filtered; washed; the filtrate evaporated to dryness and again taken up with hydrochloric acid and water; filtered and washed. The precipitates are then combined and ignited. Silicon dioxide (SiO₂) is thus formed, which can be calculated to sodium silicate (Na₂Si₄O₉). Should other metals than alkali metals be suspected present the filtrate from the silica determinations should be examined.