558 Sir H. Davy's Experiments on the 
Allen and Pepys, seems still inclined to adopt this opinion, 
though in admitting a much smaller quantity of oxygene than 
he originally supposed in charcoal ; and he considers the dia- 
mond as pure carbonaceous matter, containing, possibly, some 
atoms of water of crystallisation. 
I have long had a desire of making some new experiments 
on the combustion of the diamond and other carbonaceous 
substances, and this desire was increased by the new facts 
ascertained with respect to iodine, which by uniting to hy- 
drogene, affords an acid so analogous to muriatic acid, that it 
was for some time confounded with that substance. My object 
in these experiments, w^as to examine minutely whether any 
peculiar matter was separated from the diamond during its 
combustion, and to determine whether the gas, formed in this 
process, was precisely the same in its minute chemical nature, 
as that formed in the combustion of common charcoal. I 
have lately been able to accomplish my wishes; I shall now 
have the honour of communicating my results to the Royal 
Society, 
During a stay that I made at Florence in the end of March 
and beginning of April, I made several experiments on the 
combustion of the diamond, and of plumbago, by means of 
the great lens in the Cabinet of Natural History; the same in- 
strument as that employed in the first trials on the action of the 
solar heat on the diamond, instituted by Cosmo III. Grand Duke 
of T uscany ; and I have since made a series of researches on 
the combustion of different kinds of charcoal at Rome, in the 
laboratory of the Academia Lyncei. In the first series I was 
honoured by the assistance of the Count Bardi, the Director, 
and Signior Gazzari, the Professor of Chemistry at the 
