FIRED GUN-POWDER. 55

19x16580

cavities taken together = c = -(118) = 31502 grains,

10

and the saltpetre made use of in each of the experiments =f ;tic

then —- will express the density of the fluid contained in a

/

space—But the non-elastic substances — m which are inthe saltpetre must be deducted from /, call their bulk = r« ;

then f—rm will express the quantity of the fluid, and-

f—rm

will express the density of the elastic fluid when confined inthe saltpetre.

122. The specific gravity of the fluid generated fromnitre is supposed to be equal to the atmospheric air. Thensince the specific gravity of air to saltpetre is as 1: 1520, andthe contents of the two cavities taken together are equal to aquantity of saltpetre = c, the quantity of air in the machine(Fig. 6.) capable of producing an effect n equal to that of the

fluid s—m will be represented by the expression——. Thenf—ni-

ne

1520

and substituting in this equation the known

values c —21502, 6 grains, n — —, that of m will be

21

=4 grains ; and as the quantity of elastic fluid contained inpitre is proportionate to its mass (57), it will be expressed by

the ratio of the mass of saltpetre. It does not

follow, because the specific gravity of this fluid is equal tothe atmospheric air, that it has all the other properties of it ;much less that it is pure air : For it has been proved in theformer part of this work, that the greater the rarefaction ofthe air, the more difficultly powder is fired. Now the elasticfluid generated from the first burnt grains not supplying thawant of natural air, we must at least allow, that at the firstinstant of its generation it is deprived of the property whichthe aerial fluid possesses, of accelerating the burning of com-*bustible bodies. It would be a research foreign to our pur-pose, to enquire whether the elastic fluid does or does nosacquire this property some time after its production. -

D 4 123. In