MEANS FOR DETERMINING THE PURITY OF DRUGS, ETC. 
109 
precipitate when added to water, if sulphuret of antimony is pre- 
sent. MM. Henry and Garrot assert that sulphuret of antimony 
mixed with iodine forms a red triple compound too unlike iodine 
to answer for an adulteration. It may be only the moist iodine 
that reacts in this way. 
Clay, Sand and Slate, if present, may easily be detected by 
their insolubility in water and alcohol, and their insensibility to 
heat. 
Corrosive Sublimate. — Its great density, 5.42. satiny lustre, and 
crystalline structure, together with its solubility in ether, are 
marks by which its purity can readily be established. Both calo- 
mel and muriate of ammonia are left by the ether, as well as fused 
chloride sodium and potassium. 
Calomel, Proto-Chloride of Mercury. — Calomel is a white 
powder of sp. gr. 7.14 to 7.20 insoluble in water, alcohol, ether 
and dilute muriatic and acetic acid. It is entirely sublimed by 
heat, is converted into protoxide of mercury by an excess of heat, 
which is then wholly soluble in acetic acid. Calomel has been 
adulterated with carbonate, sulphate, and phosphate of lime, sul- 
phate of baryta, carbonate of lead and even starch and gum; it 
also sometimes contains corrosive sublimate as an impurity from 
carelessness. It is very easy for the physician and apothecary to 
assure themselves of the purity of calomel. First heat it to dull 
redness on a plate of iron ; if it all vaporizes, the above insoluble 
adulterations are absent. The calomel should then be washed with 
warm water, and if the filtered washings produce no precipitate 
with ammonia or iodide of potassium, it is free frome corrosive 
sublimate, and may be considered medicinally pure. 
If a white residue is left after the calomel is sublimed by expo- 
sure to heat, it should be treated with diluted muriatic acid ; if it 
dissolves wholly or partially with effervescence, either carbonate of 
lead or lime is probably present. If the solution is precipitated 
black by hydrosulphuret of ammonia, and yellow, by iodide of po- 
tassium, the base is oxide of lead ; if not changed by these reagents 
and is precipitated white by oxalate of ammonia, the base is 
lime. 
If the residue is more or less blackened, some organic matter 
10 
