[ 216 j 



XXXIII. On the Qnantilu of Carbon in Carbonic Acid, and 

 on the Nature of the Diamond. By William Allen, 

 Esq. F.L.S. afid William Hasledine Pepys, Esq.* 



Jl he estimates of the quantity of real carbon in carbonic 

 acid differing very widely, and the experiments of Guyton 

 de Morveau upon the combustion of the diamond, detailed 

 in the 31 St volume of the Annates de Chimie, being liable 

 to some objections from the manner in which the operatior« 

 were conducted, we determined to institute a set of experi- 

 ments, in order, if possible, to settle the question. 



Lavoisier, from the result of experiments apparently con- 

 ducted with much accuracy, concluded that every hundred 

 parts by weight of carbonic acid consisted of 28 carbon and 

 72 oxygen. This was in a great degree confirmed by the 

 very valuable researches of Smilhson Tennant, esq. on the 

 nature of the diamond, an' account of which is printed in 

 the Transactions of this Society for the year J 797, and 

 which were made previously to the experiments of Guyton j 

 but notv^fithstanding this, the result of Guyton's experiment, 

 which only allowed 17-88 percent, of carbon to carbonic 

 acid, has been adopted in all the systems of chemistry to. 

 the present time. 



In researches of this nature, the results are much in- 

 fluenced by slight variations in the quality of the gas '^ 

 but having had repeated experience of the accuracy of 

 the eudiometer (Pepys's) described in this volumef, we 

 were enabled to proceed in this respect with great confi- 

 dence. 



Oar object was, to consume certain known quantities of 

 diamond and other carbonaceous substances in oxygen gas, 

 and we at first determined to employ the sun's rays, by means 

 of a powerful lens; but considering the uncertainty of a 

 favourable opportunity in this country, and at the season in 

 which our experiments were made, we resolved to employ 

 the apparatus represented by the drawing. 



• From tl;e Trainac lions of the Rnynl Such-tij for 1807. 

 I See p. UD of the present volume of Wr Magazine. 



Dosaip- 



