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silica is obtained from this precipitate by treating it with hydro- 
chloric acid, and evaporating as usual to a dry powder. The por- 
tion of the original fused mass that is insoluble in water may also 
contain silica, and this must be removed by evaporation with 
hydrochloric acid. The equations that express the principal reac- 
tions involved are the following: 
Si0 2 + Na 2 C0 3 = Na 2 Si0 3 + C0 2 . 
Ma 2 Si0 3 + (NH 4 ) 2 C0 3 = H 2 Si0 3 + 2NH, + Na 2 Co 3 . 
But as the Si0 2 is not completely precipitated the ammoniacal 
zinc sulphate is added : 
Na 2 Si0 3 + ZnS0 4 = Na 2 S0 4 + ZnSi0 3 . 
In all these fusions, the difficulty of securing pure sodium car- 
bonate can not escape attention. The purest specimens on the 
market usually or frequently contain silica, iron and other impuri- 
ties, often in considerable quantities. To secure a proper degree of 
accuracy, the commercial article should be dissolved in pure dis- 
tilled water, filtered, and allowed to crystallize in a platinum or 
porcelain dish. If the pure sodium carbonate is not obtainable, its 
use in an analysis should be avoided whenever possible. 
SILICA BY THE LEAD OXIDE AND BORIC OXIDE METHOD OF JANNASCH . 1 
This is worthy of consideration, as it renders possible the de- 
termination of silica and the alkalies in the same sample. The 
lead oxide of commerce so frequently contains impurities that the 
substance . can better be prepared for the analysis by the ignition 
of pure lead carbonate. The carbonate is prepared by adding the 
equivalent amount of ammonium carbonate to a boiling solution of 
lead acetate. The precipitated lead carbonate is thoroughly washed 
and afterwards dried on the water bath. 
With a gram of silicate, 10 to 12 grams of lead carbonate are 
used, after mixing thoroughly with a platinum spatula. The 
crucible is gently heated at first with a small flame, and finally the 
heat is increased until fusion is complete. The substance after 
fusion is treated in the usual way, using nitric acid instead of 
hydrochloric acid. It is evaporated on the water bath to a fine 
dry powder, moistened with nitric acid, and once more evaporated 
to a fine powder. It is finally treated with concentrated nitric 
acid and water when the silica is filtered off. 
Jannasch also maintains that a silicate can be decomposed with 
pure alkali free boric oxide. The oxide to be previously fused and 
1. Chem. News, Aug. 2, 1895. 
