PREPARATIONS OF IRON. 
97 
of the sulphate, vary considerably in the relative proportions 
of the ingredients used in its formation. The United States 
pharmacopoeia orders six ounces of carbonate of soda, to eight 
ounces of sulphate of iron; the Edinburgh, five ounces of car- 
bonate of soda to four ounces of sulphate of iron; and the 
Dublin, twenty-six parts of carbonate of soda to twenty-five 
parts of sulphate of iron. 
In making a portion, I found the precipitation to be con- 
tinued after I had added eight ounces of carbonate of soda to 
eight ounces of sulphate of iron in solution, being two ounces 
more than is ordered by the United States pharmacopoeia. 
From this result, I would suggest that equal quantities of the 
two salts be used. 
Great difference in the colour, and, according to Mr. Phil- 
lips, in the composition of the product is caused by slight va- 
riations in the process for making the precipitate. 
According to Mr. Phillips, when precipitated in hot water, 
washed in hot water, and dried by steam, it contained 14.5 
per cent, of carbonic acid, and was of a chocolate brown co- 
lour; when dried in the air it contained the same quantity of 
carbonic acid, and was of a yellowish brown colour; when 
precipitated in cold water and dried by steam it contained 
one per cent, of carbonic acid, and was of a reddish brown; 
when dried in the air, no carbonic acid, and was of a yellowish 
brown colour. 
In repeating some of Mr. Phillips' experiments I have 
found the difference in colour of the several products to be 
very considerable. But the quantity of carbonic acid, though 
evidently greater in the product of the first mentioned pro- 
cess, did not differ as widely from that of the latter as in Mr. 
Phillips' experiments. 
It cannot be of great consequence which process is followed, 
but as the first is the most convenient, and as the product con- 
tains the highest proportion of carbonic acid, (to which some 
think the activity of the preparation is proportioned,) it is to 
be preferred. Eight ounces of each of the salts in crystals 
yield about three ounces of the precipitate. 
VOL. II.— no. ii. 13 
