86 On the Separation of Iron 
should know of what species it is, that he may manure accordingly, 
If siliceous, it will scratch glass: if calcareous, the acids will show 
it: if aluminous, it is so soft thatit will cut with a knife, the small 
stones are so soft, All these things are of consequence for a 
farmer to know; and a small pamphlet of this might be useful, 
with the trial of the rest. of the twenty plauts. 
] must mention, before I close this letter, that my weeds were 
all marked before they were placed in the trough with coloured 
threads, by which means I knew them again when growing up. 
I cannot think it a fair trial without the matter said to have 
been weeds is taken out and examined, to show in what state 
it is, whether really capable of manuring plants, or not. A gen- 
tleman, after letting his gardener rake out the hole, showed me 
earth which he declared had been weeds two months before; | 
only insisted on seeing the raked matter, and all the weeds which 
had not grown up were in it in a half-dying state: but in woody 
plants the folly is still more complete, and in turning-in young 
crops of beans or vetches, except the leaves that are eaten by 
vermin, all the rest remains perfect, take it out when you will, 
XVIU. On the Separation of Iron from other Metals. By 
J.F.W.Herscaer, Esq. &RS.* 
An easy and exact method of separating iron from the other 
metals with which it may happen to be mixed, has always been 
a desideratum in chemistry. Every one conversant with the 
analysis of minerals is aware of the difficulty of the problem, 
which indeed is such that, in experiments conducted on any 
thing like a large scale, it might hitherto be regarded as insu- 
perable. In consequence of this, and of the importance of the 
inquiry, there is hardly a chemist of eminence who has not pro- 
posed some process for the purpose, but (with the exception of 
that which depends on the insolubility of the persuccinate of the 
obnoxious metal, which I have not tried, and which is too ex- 
pensive to be resorted to for any but the nicer purposes of ana- 
lytical research) they are all of them either inadequate to the end 
proposed, intolerably tedious, or limited in their application. That 
which I have now to propose, on the other hand, is liable to none 
of these objections, being mathematically rigorous, of general 
application, and possessing in the highest degree the advantages 
of facility, celerity, and cheapness. It is briefly this : 
The solution containing iron is to be brought to the maxi- 
mun of oxidation, which can be communicated to it by boiling 
* From the Transactions of the Royal Society for, 1821, Part If. 
with 
