570 TESTS FOR, IMPORTANT MEDICINAL PREPARATIONS. 
The writer has seen its use abandoned upon the ground of 
idiosyncrasy, when on examination it was easily shown to 
contain a notable proportion of the irritant harsh red iodide. 
The red iodide may be easily detected in it by rubbing a 
little of the suspected iodide in a mortar with strong alcohol, 
and then allowing it a few moments to dry. The evaporation 
of the alcohol leaves the red iodide along the pestle marks as 
a border to the iodide. A minute contamination becomes 
very easily seen in this way. 
Mercury with chalk — is of late very commonly found to be 
harsh and irritant in its action, producing or increasing 
intestinal irritation to such an extent that many practi- 
tioners have abandoned its use, while others are puzzled by 
its effects. 
This also is a result of faulty preparation^ wherein through 
time and labour-saving expedients, or bad appliances, a por- 
tion of the mercury becomes oxidized instead of being simply 
comminuted or divided. However well prepared, it almost 
always contains a very small proportion of suboxide, but this 
being one of the mild preparations of mercury, never pro- 
duces the bad effects alluded to. To detect the peroxide, or 
irritating property, a drachm or two of the mixture is treated 
with an excess of acetic acid, and the solution filtered off 
clear. A few drops of hydrochloric acid is then added to the 
clear solution. If the preparation be good, this will produce 
only a slight precipitation of insoluble subchloride from the 
small quantity of acetate of suboxide formed. If the prepa- 
ration be old, or badly kept, having had free access of light 
and air, a pretty copious precipitate will be formed by the 
hydrochloric acid. The clear solution is again filtered or 
decanted off this precipitate, and liquor ammonia added to 
it. If the preparation was contaminated with any peroxide 
it will now be precipitated by the ammonia as white 
precipitate. 
Blue pill — is also liable to contain oxides of mercury, and 
thus to lose its mild character and operation through faulty 
preparation. In this the oxides are detected in precisely the 
same way as in the case of mercury with chalk. 
Iodide of potassium — is occasionally contaminated with car- 
bonate of potassa to the extent of impairing its medicinal 
effect. This is easily detected by adding lime water to the 
solution of the iodide, when carbonate of lime will be precipi- 
tated and render the mixture cloudy. 
Bitarlrate of potassa — frequently contains much tartrate of 
lime. This may be detected by stirring a few drops of liquor 
ammonia into a mixture of a few grains of the specimen in 
