ay 
390 
their analogy, than that each of 
thofe fubftances belonged to the 
clafs of inflammable bodies. 
As the nature of the diamond is 
fo extremely fingular, it feemed 
deferving of farther examination ; 
and it will appear, from the follow - 
ing expetiments, that’ it confifts 
entirely of charcoal, differing from 
the ufual ftate of that fubftance only 
by its cryftallized form. From the 
extreme hardnefs of the diamond, 
a ftronger degree of heat is required 
to inflame it when expofed merely 
to air, than’can eafily be applied in 
-Clofe vefiels, except by means of a 
ftrong burning lens ; but with nitre 
its combuftion may be effeéted in 
a moderate heat. To expofe it to 
the action of heated nitre, free from 
extraneous matters, I procured a 
tube of gold, which, by having one 
end clofed, might ferve the purpofe 
of a retort; a glafs tube being 
adapted to ‘the open end, for col- 
leéting the air produced. To be 
' Certain that:the gold veffel was per- 
feétly clofed, and that it did not 
contain any unperceived impurities 
which could occafion the produétion 
of fixed air, fome nitre was heated 
in it: till:it had become alkaline, 
and afterwards diffolved out by 
water; but the folution was per- 
dedtly free from fixed air, .as it did 
not affect the tranfparancy of lime- 
water. When: the diamond was 
deftroyed in the gold veflel by ni- 
tre; the fubftance which remained 
precipitated lime from lime-water; 
and, with acids, afforded nitrous 
vand fixed air; and it appeared fole- 
-ly to confift of nitre, partly decom- 
~pofed, and of aérated alkali. 
~ In order to eftimate the quantity 
ONE 
ANNUAL REGISTER, 1797s 
of fixed air which might be obtain- 
ed from a given weight of diamonds; 
two grains and a half of fmall dia- 
monds were weighed with great ac- 
curacy, and, being put into the 
tube, with a quarter of an ounce of 
nitre, were kept in a ftrong red 
heat for about an hour and a half. 
The heat being gradually increafed, 
the nitre was in fome degree ren- 
dered alkaline before the diamonds 
began to be inflamed; by which 
means almoft all the fixed air was 
retained by the alkali of the nitre. 
The air which came over was pro- 
duced by the decompofition of thé 
nitre, and contained fo little fixed 
air as to occafion only a very flight 
precipitation from lime-water. Af- 
ter the tube had grown cold, the 
alkaline matter contained ‘in it was 
diffolved in water, and the whole 
of the diamonds were found to have 
been deftroyed. As an acid would 
difengage nitrous air from this folu- 
tion, as well as the fixed air, the 
quantity of the latter could not, in 
that manner, be accurately deter- 
mined. To obviate this incon- 
veniency, the fixed air was’made to 
unite with -calcareous’ earth, by’ 
pouring into the alkaline folution 
a fufficient quantity of a faturated 
folution of marble in marine acid. 
The vefiel which contained them, 
being clofed, was left undifturbed. 
till the precipitate had fallen to the 
bottom ; the folution having been 
previoufly heated, that it might 
fubfide more perfeétly. The clear 
liquor being found, by means of 
lime-water, to be quite free from 
fixed air, was carefully poured off 
from the calcareous precipitate *. 
The veffel which was ufed on this 
much water had remained, a confiderable portion of the fixedair would have 
been abforbed by it. Bur, by the fame methed as that defcribed above; I obferved, 
“that as much fixed air might be obtained froma folution of mineral alkali, as by 
adding an <cid to an equal quantity of the fame kind of alkali, 
occafion 
