29 $ 
Mr. Thompson’s Experiments 
Of a 'very accurate method of proving gun-powder. 
Ail the eprouvettes , 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 circumftances 
very different from thole in which the powder is made ufe of 
in fervice. 
As the force of powder arifes from the action of an elaftic 
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 fhort 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 fufficient for the charge to be all in- 
flamed, even when the powder is of the floweft compofition, 
before the body to be .put in motion can be fenfibly removed 
from its place. The experiment, therefore, may fhew which 
of two kinds of powder is the ftrongeft, when equal quantities 
of both are confined in equal fpaces, and completely inflamed ; 
but the degree of the inflammability, which is a property effen- 
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 
