MEANS FOR DETERMINING THE PURITY OF DRUGS, ETC. 317 
white cloud indicates the presence of chlorine. The sulphate, by 
supersaturating as before, and adding solution of chloride of ba- 
rium, sulphuric acid being present, a white precipitate will fall. 
If the solution of carbonate be very strong, a white precipitate 
may form on adding solution of nitrate of silver, which will dis- 
appear on dilution ; this is also an indication of sulphuric acid, but 
not to be relied on without confirmation. 
Silicate of potassa is indicated when a solution of the carbonate 
lets fall a gelatinous precipitate on exposure to the air. It may 
be detected by saturating the salt with pure muriatic acid, evapor- 
ating to dryness and heating to redness; silicic acid is left as an 
insoluble residue when the mass is acted on by water. The silica 
frequently exists in such an amount as to form a gelatinous preci- 
pitate when the salt is supersaturated with any acid. Potasses 
carbonas should give indications with all the above tests, but not 
very decided. Potasses Carbonas Purus, no effect. This latter 
salt may give indications of silicic acid when it has undergone 
deliquescence in a white glass bottle, from dissolving some of the 
silica of the glass. 
Bicarbonate of Potassa. — A colorless crystalline solid, with a 
slight alkaline taste and reaction, with vegetable yellows. Solu- 
ble in four parts of cold water, but insoluble in boiling water 
without decomposition, carbonic acid being liberated ; insoluble 
in alcohol. By a red heat it loses about 30 per cent., or all its 
water and half its carbonic acid. The impurities to be met with 
in it are sesqui-carbonate and sulphate of potassa and chloride of 
potassium. If sesqui-carbonate be present, a dilute solution will 
form a brick red or orange precipitate, w T ith solution of corrosive 
sublimate ; sulphate of potassa and chloride of potassium may be 
detected by the same means as in the carbonate. 
Carbonate of Ammonia. — This salt is in hard translucent lumps 
of a fibrous crystalline texture; it has a strong, pungent, pene- 
trating odor and a sharp permanent taste ; its reaction is alka- 
line, and in consequence of the escape of a portion of its consti- 
tuents, moistened tumeric paper immediately becomes brown 
when held over it. It is soluble in four parts of cold water, but 
hot water decomposes it with effervescence, carbonic acid being 
liberated ; partly soluble in officinal alcohol ; in boiling alcohol 
it dissolves, but also undergoes the same change as in boiling 
