TIN IN THE PROTOSULPHATE OF IRON. 
G9 
nishes, with sulphuretted hydrogen, a precipitate from which 
metallic arsenic can be obtained. 
Tin then can disguise a small quantity of this poisonous 
metal. 
The peroxide of iron is administered in large doses. Sup- 
pose that the sulphate of iron should be sufficient to introduce 
two decigrams of tin into the stomach, the arsenic, not to be 
detected, must exist in the proportion of a milligram, and some- 
times this quantity, however small, is sufficient to establish a 
firm conviction. Suppose, likewise, that a chemist, not antici- 
pating this, should meet on the one hand a trace of arsenic, and 
on the other a large quantity of tin, he would be much embar- 
rassed. Could he affirm that the arsenic had been given as a 
poison? Does he not know that tin always contains traces of 
it? He cannot deny it; his conscience would be satisfied, but 
will justice be enlightened? These suppositions may perhaps 
be considered as exaggerated, because tin has as yet been found 
only in small quantities; but these quantities are variable, and 
it is likewise impossible to meet with a sulphate of iron 
which does not contain sufficient to give rise to like uncer- 
tainties. 
All these inconveniences have great weight in medico-legal 
research, to remedy them it would be proper, before preparing 
the hydrate, to subject the sulphate of iron to a stream of sul- 
phuretted hydrogen. Another fact, not less important, 
would likewise make this measure advisable. Arsenic, it is 
admitted, exists in certain sulphuric acids; may it not happen 
that the hydrate has been obtained from a sulphate manu- 
factured from such an acid? The new Codex prescribes 
purified sulphate of iron; the term purified embraces, it is 
true, the whole ground; but how many persons are there who 
see in purification nothing more than solution, filtration, and 
crystallization, and these means are here totally insufficient. 
Journ. de Pharmacie. 
