372 Aiialt/sis of Scientific Books. 



served on all the four sides. Should such a project take place, it will be 

 best to take the stations at about one fourth of its altitude above the base, 

 that being the place where the deviation of the plummet would be the 

 greatest. Finally, so favourable for such an experiment do those circum- 

 stances appear, aud so anxious are my vf ishes for its completion and success, 

 that, were it not for my great age and little health, 1 should be glad to 

 make one in any party to undertake such an expedition. 



7. On the Separation of Iron from other Metals. By J. F. W. 

 Herschel, Esq. 



The following is Mr. Herschel's mode of proceeding : 



The solution containing iron is to be brought to the maximum of oxi- 

 «latiou, which can be communicated to it by boiling with nitric acid. It 

 is then to be just neutralized while in a stale of ebullition, by carbonate of 

 ammonia. The whole of the iron to the last atom is precipitated, and the 

 ■whole of the other metals present (which 1 suppose to be manganese, 

 cerium, nickel, and cobalt), remains in solution. 



The precautions necessary to ensure success in this process are few and 

 simjile. In the first place, the solution must contain no oxide of manganese 

 or cerium above the first degree of oxidatioDt otherwise it will be sepa- 

 rated with the iron. It is scarcely probable in ordinary cases that any 

 such should be present, the protoxides only of these metels forming salts 

 of any stability; but should they be suspected, a short ebullition with a 

 little sugar will reduce tiiem to the minimum. If nitric acid be now added, 

 the iron alone is per-oxidized, the other oxides remaiuing at theminimimi. 

 Moreover, in performing the precipitation the metallic solution should not 

 be too concentrated, aud must be agitated the whole time, especially towards 

 the end of the process ; aud when the acid re-action is so far diminished 

 that log-wood paper is but feebly affected by it, the alcaliue solution must 

 lie added cautiously, in small quantities at a time, and in a diluted state. 

 If too much alcali be added, a drop or two of any acid will set all right 

 again ; but it should be well observed, as upon this the whole rigonr of the 

 process depends, that no inconvenience can arise from slightly surpassing 

 the point of precise neutralization, as the newly precipitated carbonates of 

 the above etiumerated metals are readily soluble, to a certain extent, in the 

 solutions in which they are formed (though perfectly neutral). In the cases 

 of cobalt and cerium, this re-dissolution of the recent precipitate formed by 

 carbonate of ammonia is very considerable, and a solution of either of 

 these metals, thus impregnated with the metallic carbonate, becomes a test 

 of the presence of peroxide of iron, of a delicacy surpassing most of the 

 re-ageuts used in chemistry, the minutest trace of it being instantly thrown 

 down by them from a boiling solution, provided no marked excess 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 

 liquid, while hot, with a drop of the alcaline 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 neutralization performed anew. 



Such of our chemical readers as may be concerned in the 

 analysis of ferruginous compounds, will find some remarks 

 on the subject in the observations which follow the above 

 extract. 



