NOTES ON THE PHARMACOPEIA. 
397 
retted hydrogen gas when acted on by acids, to a sufficient extent to materially 
influence the result of its action. A test ought, therefore, to be given for indi¬ 
cating this defect when it occurs. 
A slight modification might also with advantage be made in the process for 
its production, by which freedom from the presence of sulphur in the product 
may be more completely ensured than it is in the process as at present given. 
It is directed to be made by exposing hydrated peroxide of iron at a red heat to 
the reducing action of hydrogen gas ; but, as the hydrated peroxide of iron of 
the Pharmacopoeia is made by precipitation from a solution of persulphate of 
iron with caustic soda, this, as produced by manufacturers, generally retains a 
small portion of sulphate, which is not completely washed out in the process, 
and this sulphate is afterwards reduced to sulphide by the hydrogen during the 
conversion of the oxide to reduced iron. The liability to such a result would be 
obviated if the oxide used in the process were directed to be obtained from chlo¬ 
ride of iron by precipitation with ammonia. 
Hydrargyri Iodidum Viride. —It is deserving of consideration whether this 
preparation should not be omitted from the Pharmacopoeia, on account of its 
great liability to change. 
Hydrargyrum Ammoniatum. —This preparation, the white precipitate of phar¬ 
macy, is directed in the Pharmacopoeia to be made by adding ammonia to a 
solution of corrosive sublimate. There is, however, another method of prepa¬ 
ring white precipitate, which consists in using sal ammoniac and carbonate of 
soda in the place of ammonia ; but when made by this process the product, 
although similar in appearance to the other, differs in composition, and con¬ 
tains a smaller proportion of mercury. It has been shown that some of the 
white precipitate of commerce has the composition and properties of that made 
with sal ammoniac, and, as the process by which this is produced is less costly 
than the other, the product obtained by it from a given quantity of perchloride 
of mercury being greater, there is an inducement for manufacturers to adopt it. 
The Pharmacopoeia preparation may be distinguished from that made with sal 
ammoniac by the fact that it may be entirely volatilized on the application of 
heat without its being fused , while the unauthorized preparation fuses before it 
volatilizes. This property ought to be indicated among the tests given in the 
Pharmacopoeia. 
Linimentum Potassii Iodidi cum Sapone. —Some alteration in the directions 
for preparing this liniment appears to be called for, as much difficulty has been 
experienced by practical pharmaceutists in producing satisfactory and uniform 
results from the process as described in the Pharmacopoeia. 
The processes for some of the other liniments, such as Linimentum Hydrargyri 
and Linimentum Terebinthinse Aceticum , would also admit of improvement. 
Liquor Magnesite Carbonatis. —This preparation would, I think, be improved 
by reducing its strength. The process as given in the Pharmacopoeia yields a 
solution containing thirteen grains of carbonate of magnesia to the fluid ounce, 
but it can only be kept of this strength while it is fully charged with carbonic 
acid gas. On exposure to the air, some of the gas escapes, and carbonate of 
magnesia is then deposited. A solution containing ten grains of carbonate of 
magnesia in the ounce would be more easily made, and much more easily kept 
for use without alteration of strength. , 
Opium. —The great importance of opium as a therapeutic agent, and as the 
source from which many valuable medicines are produced, and the variation in 
strength and composition to which the commercial drug is subject, render it 
very desirable that those who use opium in the preparation of medicines should 
test its strength before applying it for such purpose. A method of doing this is 
described in the Pharmacopoeia, but the test given occupies so much time in its 
application that, even if in other respects it be unobjectionable, this would 
