125 
Nature of the Diamond . 
and that it did not contain any unperceived impurities which 
could occasion the production of fixed air, some nitre was heated 
in it till it had become alkaline, and afterwards dissolved out 
by water ; but the solution was perfectly free from fixed air, 
as it did not affect the transparency of lime-water. When the 
diamond was destroyed in the gold vessel by nitre, the sub- 
stance which remained precipitated lime from lime-water, and 
with acids afforded nitrous and fixed air; and it appeared 
solely to consist of nitre partly decomposed, and of aerated 
alkali. 
In order to estimate the quantity of fixed air which might 
be obtained from a given weight of diamonds, two grains and 
a half of small diamonds were weighed with great accuracy, 
and being put into the tube with a quarter of an ounce of nitre, 
were kept in a strong red heat for about an hour and a half. 
The heat being gradually increased, the nitre was in some de- 
gree rendered alkaline before the diamond began to be in- 
flamed, by which means almost all the fixed air was retained 
by the alkali of the nitre. The air which came over was pro- 
duced by the decomposition of the nitre, and contained so little 
fixed air as to occasion only a very slight precipitation from 
lime-water. After the tube had grown cold, the alkaline 
matter contained in it was dissolved in water, and the whole of 
the diamonds were found to have been destroyed. As an acid 
would disengage nitrous air from this solution as well as the 
fixed air, the quantity of the latter could not in that manner be 
accurately determined. To obviate this inconvenience, the fixed 
air was made to unite with calcareous earth, by pouring into 
the alkaline solution a sufficient quantity of a saturated so- 
lution of marble in marine acid. The vessel which contained 
