108 
MEANS FOR DETERMINING THE PURITY OF DRUGS, ETC. 
carbonate of potassa, neutralizing the filtered solution with acetic 
acid and precipitating the chlorine as chloride of silver. 
Cyanide of Iodine. — Dr. Herzog thinks that " the presence of 
cyanogen is due to the small marine animals, which are always 
unintentionally, or to the larger ones, which are intentionally 
mixed up with the sea plants from which kelp is prepared, and 
which upon being heated, form combinations of cyanogen with 
the carbonate of soda of the ashes." The presence of cyanogen 
is determined by dissolving the suspected iodine in a solution of 
pure potassa, evaporating to dryness, heating to redness to de- 
compose the iodate and cyanate of potassa, dissolving again in 
water, adding a mixture of sesqui and proto-chloride of iron till it 
ceases to precipitate. This precipitate is then treated with muri- 
atic acid, and if any cyanogen was present, it will remain undis- 
solved, as prussian blue (ferrocyanide of iron.) The directions of 
the new Dublin Pharm., (see p. 12 of this volume,) to subject 
iodine to a preliminary sublimation, has reference to the presence 
of cyanide of iodine, which constitutes the white acicular crystals 
referred to. 
The Chlorides of Calcium and Magnesium are easily detected 
by the loss of weight which the iodine sustains when agitated 
with water, and by evaporating the aqueous washings to dryness, 
the amount of the impurity may be arrived at. If both chlorides 
are present, they can be separated by adding an excess of solution 
Of bicarbonate of potassa, which precipitates the lime as carbo- 
nate, when the magnesia may be precipitated from the filtered 
solution by adding the carbonate of potassa in excess. Both of 
these adulterations are soluble in alcohol, and cannot be detected 
by the solubility of the suspected iodine in that fluid. 
Plumbago is detected by its insolubility in alcohol, and by its 
sensitiveness to the attraction of the magnet, which will separate 
it from oxide of manganese, coal, charcoal, sulphuret of antimony, 
galena, sand and clay. 
Black Oxide of Manganese. — If the black insoluble residue of 
the suspected iodine evolves chlorine when treated with muriatic 
acid, this oxide is present. 
Sulphur ets of Antimony and Lead may be detected in the resi- 
due, if present by the action of muriatic acid, which disengages 
sulphuretted hydrogen. The muriatic solution will cause a white 
