MEANS FOR DETERMINING THE PURITY OF DRUGS, ETC. Ill 
tity of ferrocyanuret used should not be sufficient to give a yellow 
color to the solution. Chloride of magnesium is sometimes pre- 
sent, and gives a deliquescent character to the salt. If, by acting 
on sulphate of magnesia by alcohol, and evaporating the spirit, a 
solid residue be obtained, this chloride may be present and then 
this residue dissolved in water will yield with nitrate of silver, a 
white precipitate insoluble in nitric acid. Sulphate of soda is de- 
tected with more difficulty. If the salt be unusually efflorescent it 
may be suspected. One hundred grains dissolved in boiling water 
and decomposed completely by a hot solution of carbonate of soda, 
will yield a precipitate of carbonate of magnesia, which, when 
washed and dried, should weigh thirty-four grains; any deficiency 
would indicate sulphate of soda in proportion to the amount. 
Sulphate of Copper.— This salt forms translucent deep sapphire- 
blue crystals which effloresce slightly, becoming covered with a 
green incrustation ; when moderately heated they lose water of 
crystallization, and fall into a pale blue powder. They are solu- 
ble in four parts of cold water, but insoluble in alcohol. The caus- 
tic and carbonated alkalies produce green precipitates in solution, 
of sulphate of copper, which are redissolved by an excess of ammo- 
nia and its carbonate. Sulphate of copper frequently contains 
iron, and sometimes in considerable amount. This may be detect- 
ed by supersaturating its solution with liquor ammoniee, when all 
the oxide of copper will be redissolved, and greenish black, or 
brown flocculi will be left, if iron be present. These flocculi are 
not distinct, if the iron be as protoxide or in small amount, the 
intense blue of the solution rendering them almost invisible; their 
presence may be set beyond doubt by filtering the deep blue solu- 
tion and washing, when the oxide of iron will coat the inside of 
the filter with a yellow or brown film. Sulphate of zinc is said 
sometimes to be contained in sulphate of copper. To ascertain this, 
a solution of the salt is to be precipitated by solution of potassa, 
and an excess added by which the oxide of copper will not be 
touched, while any oxide of zinc will be redissolved ; on filtering 
and adding to the clear liquid, a solution of bicarbonate of po- 
tassa or soda sufficient to convert the caustic into carbonate of po- 
tassa, white flocculi of oxide of zinc will appear. The solution 
of bicarbonate should be added very carefully with agitation, an 
