320 
MEANS FOR DETERMINING THE PURITY OF DRUGS, ETC. 
acid, and oxalates if it contains lime, and oxide of iron may be 
detected by nearly neutralizing the acid solution and adding ferro- 
cyanuret of potassium, when a blue color will result. 
Carbonate of Baryta. — The native carbonate of baryta, is offici- 
nal as a means of preparing chloride of barium. It is in yellowish 
fibrous masses, somewhat translucent ; insoluble in water ; soluble 
in muriatic acid with effervescence, leaving no residue. It may 
contain sulphate of baryta and carbonates of strontia and lime. 
The former will be left as a heavy insoluble residue after the action 
of muriatic acid ; strontia will be detected by evaporating the solu- 
tion in muriatic acid to dryness, and adding alcohol ; on setting 
fire to the mixture, a red edge to the flame will be given, although 
the quantity of strontia present may be small. If lime be present, 
sulphuric acid in excess will precipitate all the baryta from the 
solution in muriatic acid, when the addition-of solution of carbonate 
of soda will throw down a white precipitate of carbonate of lime, 
especially if the solution be raised to boiling point, to ensure the 
absence of an excess of carbonic acid. In the form of powder, it 
may contain sulphuret of lead, with wmich it is associated as a 
mineral ; the muriatic acid will cause the evolution of the sulphu- 
retted hydrogen, and sulphuretted hydrogen will produce a black 
precipitate when passed through the solution ; solution of ammo- 
nia also produces a white precipitate not soluble in an excess. 
Carbonate of Zinc. — Officinal under two forms, Calamina or 
impure native carbonate, and zinci carbonas pracipitatus. 
Calamine, as intended in the Pharmacopoeias, is that variety of 
the mineral which is composed chiefly of carbonate of zinc. It is 
when prepared in fine powder, varying in color from yellowish 
white to brownish yellow. In its purest form, it is totally soluble 
in diluted sulphuric acid with effervescence ; generally it leaves an 
insoluble residue, derived from the adhering matrix. As for 
convenience of powdering, it is heated red hot, the effervescence is 
not great, on account much of the carbonic acid having been driven 
off. The solution produces a gelatinous precipitate with ammonia, 
nearly all soluble in an excess. 
This article is commonly adulterated, or more properly spurious 
mixtures are substituted for it, to such an extent, that it is difficult 
to obtain a preparation under this name, containing any zinc. The 
factitious mixture generally contains sulphate of barytes, carbonate 
