1821.] Proceedings of Philosophical Societies, 389 



-Now here it is to be observed, that Capt. K/s conjecture is 

 misrepresented, as will be clear from a reference to his own 

 words, Phil. Trans. 1819, Part III. p. 425: 



*^ It would be no improbable conjecture, that the sudden 

 increase of gravitation, observed at Arbury Hill, may be occa- 

 sioned by a rock of primitive formation approaching the surface 

 of the earth in the vicinity of that station." 



He then subjoins in a note, *' I find the conjecture I have 

 hazarded remarkably supported by fact ; for on consulting 

 Smith's Geological Ma}> of England, it appears that Mount 

 Sorrel, a mass of granite, is situated, together with other rocks 

 of primitive formation, about 30 miles to the N of Arbury Hill." 



This is surely very different from saying that the attracting 

 mass is Mount Sorrel. That rock is obviously mentioned only 

 to show the probability that granite may form the substratum of 

 some point near the place of observation. 



/ 



Article XII. 



Proceedings of Philosophical Societies, 



ROYAL SOCIETY. 



April 5. — A paper was read, *' On the Separation of Iron 

 from other Metals," by J. F. W. Herschel, Esq. 



Mr. Herschel proposes, as the basis of a rigorous separation 

 of iron from the metals not precipitated by sulphuretted hydro- 

 gen which it most usually contaminates (manganese, cerium, 

 nickel, and cobalt), a peculiarity in the peroxide of iron, in virtue 

 of which it is incapable of subsisting in a neutral solution at the 

 boiling temperature. If a solution of this peroxide be neutral- 

 ized when cold, and then heated, a portion is deposited in the 

 state of a subsalt, and the hquid becomes acid. If allowed to 

 cool, and again neutralized, a fresh portion of the metallic con- 

 tents separates on re-applying the heat, and so on, till the quan- 

 tity held in solution is no longer sensible to the most dehcate 

 reagents. If, on the other hand, the neutralization be performed 

 while actually boilings we attain this limit at one operation. 

 Hence Mr. Herschel recommends the following process : Having 

 peroxidized, by means of nitric acid, a solution containing iron 

 and any of the above-mentioned metals, drop into it, while boil-' 

 ing, carbonate of ammonia, till the acid reaction is entirely 

 destroyed, and even going a little bei/ond the point of exact neu- 

 tralization. The whole of the iron to the last atom is sepa- 

 rated, while the liquid retains in solution the other metallic 

 oxides, as well as the minute portion of their carbonates due to a 



