Mr. Thompson’s Experiments 
Of a very accurate method of proving gun-powder. 
All the epr ouveties . , or powder-triers, in common ufe are de- 
fective in many refpects. Neither the abfolute force of gun- 
powder can be determined by means of them, nor the compa- 
rative force of different kinds of it, but under circumfrances 
very different from thofie in which the powder is made ufe of 
in fervice. 
As the force of powder arifes from the action of an eladic 
fluid that is generated from it in its inflammation, the quicker 
'the charge takes fire, the more of this fluid will be generated 
in any given Ihort fpace of time, and the greater of courfe will 
be its effedt upon the bullet. But in the common method of 
proving gun-powder, the weight by which the powder is con- 
fined is fo. great in proportion to the quantity of the charge, 
that there is time quite fu fficient ffor the charge to be all in- 
flamed, even when the powder is of the flowed: compofition, 
before the body to be put in motion can be fenfibly removed 
from its place. The experiment, therefore, may fiiew which 
of two kinds of .powder is the.dronged, when equal quantities 
of both are confined in equal fpaces, and completely inflamed .; 
but the degree of the inflammability, which is a property efifen- 
tial to the goodnefs of the powder, cannot by thefe means be 
afcertained. 
Hence it appears, how powder may anfwer to the proof, 
fuch as is commonly required, and may neverthelefs turn out 
very indifferent when it comes to be ufed in fervice. And this, 
I believe, frequently happens; at lead I know complaints 
from officers of the badnefs of our powder are very common ; 
. and I would fuppofe that no powder is ever received by the 
6 Board 
