An Advanced Course in Quantitative Analysis

(sp. gr. 1.12), heating to aid the solution. Filter off the insoluble residue, and wash first with dilute hydrochloric acid and afterward with hot water. Ignite the paper and residue at a low temperature, and weigh approximately within 5 milligrams. Cover with six times the weight of sodium carbonate and fuse until action ceases. Add a few cubic centimeters of water to the crucible and warm, then wash the contents of the crucible into the original acid solution. Evaporate to dryness on the steam table, moisten the dried mass with 1 or 2 cc. of hydrochloric acid (sp. gr. 1.20), and again evaporate to dryness. Place in a hot closet and keep at a temperature of noC. for one-half hour to dehydrate the silica. Moisten the residue with 5 cc. of strong hydrochloric acid and warm. Then add 50 cc. of water and heat until solution is complete. Filter immediately, wash the silica with dilute hydrochloric acid (one part acid, sp. gr. 1.12, to three parts of water) until the filter shows no traces of iron, and then finally with hot water. Evaporate the filtrate for the recovery of traces of silica, as was done in the silicate analysis. Ignite both filters in a platinum crucible and weigh. Treat the ignited silica with one or two drops of water, enough hydrofluoric acid to dissolve it, and two drops of sulphuric acid (1 : 1). Evaporate to dryness in a hydrofluoric acid burner, ignite, and weigh again. The difference in weight represents the silica. The weight of the residu...