140 
Book I. 
ANALYSIS OF 
the action of the surrounding air. Scheele found, that 
under these circumstances 10 parts of plumbago were 
sufficient to decompose 96 parts of nitre, and Mr Kir 
wan found, that nearly the same quantity of charcoal 
was sufficient for producing the same effect. 
Macquer long ago observed that no volatile oily 
matter will detonate with nitre, unless it be previously 
reduced to a charcoal; and that then its effect upon 
nitre is precisely proportional to the charcoal which it 
contains *. Mr Kirwan, upon trying the experiment 
with vegetable pitch and maltha, found that these sub 
stances did not detonate with nitre, but merely burn 
upon its surface with a white or yellow flame ; and 
that after they were consumed, nearly the same quan 
tity of charcoal was necessary to decompose the nitre 
which would have been required if no bitumen had 
been used at all†. Now coals are chiefly composed of 
charcoal and bitumen. It occurred therefore to Mr Kir 
wan, that the quantity of charcoal which any coal con 
tains may be ascertained by detonating it with nitre : 
For since the bitumen ôf the coal has no effect in de 
composing nitre, it is evident that the detonation and 
decomposition must be owing to the charcoal of the 
coal; and that therefore the quantity of coal necessary 
to decompose a given portion of nitre will indicate the 
quantity of carbon which it contains : and the propor 
tion of charcoal and earth which any coal contains be 
ing ascertained, its bituminous part may be easily had 
from calculation. 
The crucible which he used in his experiments was 
large ; it was placed in a wind furnace at a distance 
Miner. il. 522. 
* Macquer's Dictionary, Second Edit. p. 481.