ON THE DOUBLE SALTS OF IRON. 
nation notice should be taken that the salt was dry, for it is 
of so deliquescent a nature, that by long keeping, or trans- 
ferring from one bottle to another, it absorbs water. I was 
sorry, therefore, to find, by his note to me, that he had tried 
the salt in the state I sent it to him. It is true, he remark- 
ed, that the salt appeared quite dry, but there might have 
been water, and my impression is, there was, and that his 
estimate is too low : under these circumstances, I think I 
am entitled to split the difference, and call it thirty-five. 
I submit it to you whether I may not with reason infer 
that the real constitution of this salt is one equivalent of 
citrate of iron, and one equivalent of citrate of ammonia ; 
that is, ' 
Sesquioxide of Iron, 80 or 37.56 
Citric Acid, 116 " 54.46 
Ammonia, 17 " 7.9S 
Equivalent, 213 100.00 
What now forces itself upon the mind — what but the 
conviction that these two compounds are the representatives 
of two distinct series of chalybeate salts ? I anticipate the 
objection that I do not show by analysis that my theory is 
exactly confirmed. It is true, I come only very near the 
point, but I ask, let it be recollected that these salts are tin- 
crystallizable; that on this account it is most difficult to keep 
the one series from interfering with the other ; and this prac- 
tical difficulty has been the cause, I think, of the uncer- 
tainty of opinion that is current among us. 1 show two 
compounds, one containing very nearly one equivalent of 
oxide of iron united to one equivalent of acid, the other 
containing one equivalent of oxide of iron united to two 
equivalents of acid : they have peculiar external charac- 
ters, and are arrived at by different means. I point out 
how this "not quite" is to be explained, and I do think that 
in forming my opinion I have followed closely in the track 
