MEANS FOR DETERMINING THE PURITY OF DRUGS, ETC. 
319 
ing readily and soon subsiding ; solution transparent and color- 
less. Not well washed it may contain chlorides of sodium and 
calcium, or carbonate of soda and chloride of sodium. Washed 
with water, the filtered liquid, if chloride of calcium be present, 
will produce white precipitates with solution of nitrate of silver 
and oxalate of ammonia; carbonate of soda will be indicated 
when the above liquid turns the yellow of tumeric to brown. It 
may also contain iron and magnesia. In this case its solution is 
hydrochloric acid, rendered nearly neutral by an alkali, will indi- 
cate iron by producing a greenish or blue color with ferrocyanuret 
of potassium. Magnesia may be detected by adding to the solu- 
tion in hydrochloric acid (an excess of acid being used) carbonate 
of ammonia, filtering and heating the clear liquid to the boiling 
point, to drive off any carbonic acid which may hold carbonate of 
lime in solution, filtering again if necessary, and adding phosphate 
of soda. A crystalline precipitate gradually forms if magnesia be 
present. 
If prepared chalk or shell be substituted for, or mixed with, the 
precipitated carbonate, the permanency of the froth and the un- 
dissolved flocculi will be sufficient to discriminate this imposition. 
Sulphate of lime is also said to be used as an adulteration; in this 
case, there will be a residue left after the action of the acid in 
varying amounts, very slightly soluble in water. 
Carbonate of Magnesia is in light, white, spongy masses, 
smooth to the touch, inodorous, tasteless, and insoluble. Thrown 
into dilute muriatic acid, it dissolves readily, with effervescence, 
forming a clear solution. At a red heat it loses about 58 per 
cent of its weight. The impurities present, may be soluble or 
insoluble in water. The former, the alkaline chlorides, sulphates, 
and carbonates, may be detected by boiling some of the carbonate 
in water and testing the filtered liquid with nitrate of silver, which 
will afford a white precipitate, if the chlorides, chloride of barium, 
a white precipitate if sulphate, and solution of turmeric, which 
will become brown if carbonate of an alkali are present The 
insoluble impurities are alumina, lime and oxide of iron ; its solu- 
tion in hydrochloric acid yielding with ammonia added in such 
excess as to retain in solution all the magnesia ; a gelatinous pre- 
cipitate soluble in caustic potassa indicates "alumina. The solu- 
tion neutralized by ammonia, forms a white precipitate with oxalic 
