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XIV. On the Quantity of Carbon in carbonic Acid, and on the 
Nature of the Diamond. By William Allen, Esq. F. L. S. and 
William Hasledine Pepys, Esq. Communicated by Humphry 
Davy, Esq. Sec. R. S. M. R. I. A. 
Read June 18, 1807. 
The 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 
31st volume of the Annales de Chimie, being liable to some 
objections from the manner in which the operations were con- 
ducted, we determined to institute a set of experiments, 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 
oxygene. This was in a great degree confirmed by the very va- 
luable researches of Smithson Tennant, Esq. on the nature of 
the diamond, an account of which is printed in the Transactions 
of this Society for the year 1797, and which were made previ- 
ously to the experiments of Guyton ; but notwithstanding this, 
the result of Guyton’s experiment, which only allowed 17,88 
per cent, 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 influenced 
by slight variations in the quality of the gas ; but having had re- 
peated experience of the accuracy of the eudiometer described 
