40 6 Dr. ingenhousz’s Account of a 
flame of the two airs; and thus the conflagration fpreads 
with a very great velocity through the whole mafs, though 
always by fucceffion. The quicknefs of this propagation 
of fire depends in a great ineafure upon the intervals or 
interftices which remain among the grains of gunpow- 
der, through which the particles of heated charcoal 
are driven in every direction, together with the flame of 
the two airs. Hence gunpowder reduced into impalpable 
powder, and rammed into a fquib, does not inflame with 
an explofion, but burns flowly farther and farther till 
the combuftion reaches the extremity of the fquib, where 
it meets a mafs of gunpowder in grains, when imme- 
diately a loud explofion iffues, by which the fquib is 
ftiattered into rags. Hence the fize of the grains of gun- 
powder muft be proportionate to the fize of the fire 
arms to which it is deftined, the greateft fire arms re- 
quiring in general grains of the largefl: fize. 
If this wonderful and awful ingredient had not been 
difcovered by accident, could the fecret have efcaped a 
long while the penetration of our modern philofophers, 
who have found out the way of combining the air of the 
two conftituents after they had extricated them, without 
any regard to the known properties of gunpowder? No- 
thing more was to be done than combining the two fub- 
4 fiances 
