10 Biegraphical Account of [JuLY, 
During the course of the year 1796 Mr, Tennant communicated 
to the Royal Society his paper on the nature of the Diamond. Sir 
Isaac Newton had conjectured that this body was inflammable, as 
was afterwards proved by the experiments of the Duke of Tuscany 
and of Messrs. Darcet and Rouelle. M. Lavoisier effected its 
combustion by means of a lens, in close vessels, and obtained from 
it a gas, which precipitated chalk from lime-water. But this was 
at an early period of pneumatic chemistry; and although he con- 
cluded that the gas was fixed air, yet he did not consider the 
analogy between charccal and the diamond as very intimate, but as 
depending only on their common property of being combustible. 
The merit of completely ascertaining the nature of this substance 
was therefore reserved for Mr. Tennant. He succeeded in burning 
the diamond when reduced to powder, by heating it with nitre in a 
gold tube. A solution of the alkaline salt was then poured into 
liquid muriate of lime; and the quantity of carbonic acid which 
had been generated was inferred from the weight of the precipitate, 
which was found to consist of carbonate of lime. 
From experiments made upon minute quantities of diamond 
powder, not exceeding 21 grains, he shewed, by comparing them 
with Lavoisier’s experiments on charcoal, that equal weights of 
diamond and charcoal yield equal quantities of fixed air, and that 
fixed air contains between 27 and 27°8 per cent. of diamond ; 
results which very nearly agreed with those of M. Lavoisier, and 
were subsequently confirmed by the investigations of Messrs. Allen 
and Pepys. 
In the course of his investigation of the diamond, Mr. Tennant 
observed that gold and platina were corroded and dissolved by heated 
nitre ; and that on the addition of water to the salt, the metals, 
owing to the presence of nitrite of potash, were in a great measure 
precipitated. ‘These appearances, together with some peculiar pro- 
perties of the nitrous solutions of gold, were the subject of a fur- 
ther communication to the Royal Society in 1797. 
It is worthy of remark, that Mr. Tennant had ascertained the 
true nature of the diamond some years before he made the above 
communication to the Royal Society. In conversing about this 
time with a particular friend, whom he was attending with affec- 
tionate care during a lingering illness in the spring of 1796, he hap- 
pened to mention the fact of this discovery. His friend, who had 
often lamented Mr. 'S’.’s habits of procrastination, urged him to Jose 
ho time in making his experiment public; and it was in conse- 
quence of these entreaties that the paper on the diamond was pro- 
duced. A still more remarkable exainple of the same indolence or 
inattention occurred in the case before alluded to of the paper on 
double distillation, communicated to the Royal Society in 1814, 
the substance of which he had mentioned to some of his friends 
during his residence at Cambridge. 
These facts are memorable and instructive instances of the 
strength and weakness of Mr, Tennant’s mind. His curiosity and 
activity were incessant; he had a vigilance of observation which 
