V 
Mr Herschers Process for Separating Iron from Metals. 301 
The precautions necessary to insure success in this process, 
are few and simple. In the first place, the solution must com 
tain no oxide of manganese or cerium above the first degree of 
oxidation, otherwise it will be separated with the iron. It is 
scarcely probable, in ordinary cases, that any such should be 
present, the protoxides only of these metals forming salts of any 
stability ; but should they be suspected, a short ebullition with 
a little sugar will reduce them to the minimum. If nitric acid, 
&c. be now added, the iron alone is peroxidised, the other oxides 
remaining at the minimum. Moreover, in performing the pre- 
cipitation, the metallic solution should not be too concentrated, 
and must be agitated the whole time, especially towards the end 
of the process ; and when the acid re-action is so far diminished, 
that logwood paper is but feebly affected by it, the alkaline so- 
lution must be added cautiously, in small quantities at a time, 
and in a diluted state. 
If too much alkali be added, a dmp or two of any acid will 
set all right again ; but it should be v/ell observed, as upon this 
the whole vigour of the process depends, that no inconvenience 
can arise from slightly surpassing the point of precise neutralisa- 
tion, as the neidy precipitated carbonates of the above concen- 
trated metals are readily soluble to a certain extent in the solu- 
tions In which they are formed, ( though perfectly neutral ). 
In the cases of cobalt and cerium, this re-dissolution of the re- 
cent precipitation formed by carbonate of ammonia, is very con- 
siderable, and a solution of either of these metals thus impreg- 
nated with the metallic carbonate, becomes a test of the presence 
of peroxide of iron, of a delicacy surpassing most of the re-agents 
used in chemistry^, the minutest trace of it being instantly thrown 
down by them from a boiling solution, provided no marked ex- 
cess of acid be present. To be certain, however, that we have 
not gone too far, it is advisable, after separating the ferruginous 
precipitate, to test the clear liquor, while hot, with a drop of 
the alkaline carbonate. If the cloud which this produces be 
clearly re-dissolved, on agitation, we may be sure that only iron 
has been separated. If otherwise, a little acid must be added, 
the liquor poured again through the filter, so as to wash the 
precipitate, and the neutralisation performed anew.— -P, 29*5. 
