1823.] New Scientific Books. 77 



of pig-iron is about 7'6, and that of black-lead is 2, or less. Now the 

 bulk of black-lead procured in the experiment is equal to that of the 

 original iron exposed to solution. Two such bodies could not co-exist 

 in the same space, or, if that could be imagined, the specific gravity of 

 such iron must be far more different from that of pure iron than it is. 

 If pure iron indeed is freed from the effects of condensation by heating, 

 it scarcely differs in specific gravity from pig-metal. Thus while we 

 conclude that the plumbago combined with the iron is a metal, we may 

 also infer that the specific gravity of that metal is not very different from 

 that of iron." 



Upon this theory we trust that Dr. Mac Culloch will excuse our 

 offering the following remarks : In the first place, nothing but carbon 

 has been detected in the diamond by the most refined and delicate 

 investigations of chemistry, those of Sir H. Davy, Messrs. Allen ami 

 Pepys, and others: that gem, therefore, must be a form of Dr. M.'s 

 new metal ; now if black-lead be its oxide, supposing it to contain only 

 one atom of oxygen, then, when equal weights of each substance are 

 burnt in oxygen gas, the former should require, for its complete con- 

 version into carbonic acid, twice as much oxygen as the latter; but the 

 experiments of Messrs. Allen and Pepys have demonstrated, that both 

 these substances require for their combustion precisely the same volume 



of oxygen. 



Secondly, Dr. Mac Culloch does not seem to be aware of the exist- 

 ence of silicium in cast-iron. The experiments of Mr. Daniell, recorded 

 in vol. ii. of the Journal of Science, show that the absorption of oxy- 

 gen, and the consequent evolution of heat, by the black-lead separated 

 from the metal, is owing to the conversion of silicium into silica, and 

 not to that of any unknown principle into black-lead. 



We are not sure that we understand the concluding argument, but 

 does it not indicate, either that Dr. Mac Culloch considers cast-iron to 

 be a mechanical mixture of carbon and the metal, or that he thinks, 

 (which is likewise contrary to the known fact), that the arithmetical 

 mean of the specific gravities of the ingredients of a compound is the 

 true specific gravity of the compound itself? 



Article XII. 

 NEW SCIENTIFIC BOOKS 



PREPARING FOR PUBLICATION. 



A Narrative of a Voyage round the World in the Uranie, Capt. 

 Freycinet, dispatched on a Scientific Expedition by the French Go- 

 vernment during the Years 1817, 1818, 1819, and 1820; in a Series of 

 Letters to a Friend. By, J. Arago, Draftsman to the Expedition. 

 The Work will form a Quarto Volume, embellished with 2G Engrav- 

 ings. 



A Description of an Antediluvian Den of Hyaenas, discovered at 

 Kirkdale, in Yorkshire, in 1821 , and containing the Remains of the 

 Hyaena, Tiger, Bear, Elephant, Rhinoceros, Hippopotamus, and 16 

 other Animals, all formerly Natives in this Country. With a Compaq 



