1874.] British Artillery Matériel. 43 
2. When a charge of any description of powder is in- 
creased beyond a certain limit, wave or local pressures are 
set up which strain the gun unduly, without affording an 
equivalent of useful effect on the projectile. 
3. Provided the battering charge is not exceeded, the 
pressure in the gun increases steadily with the increment 
in weight of the projectile up to a certain point; beyond 
this point no material increase of pressure can be obtained 
by increasing the weight of the projectile. 
4. Proof of pebble powder of Waltham Abbey and trade 
manufacture in accordance with specification. 
This proof has been carried on with the 8-inch smooth- 
bored gun prepared for the purpose. The Committee con- 
sider the results to be on the whole very satisfactory, and 
express their unanimous opinion that the velocity and 
pressure test of powder for heavy guns should never be 
suspended, as they are satisfied it is the only proof that 
will ensure the supply of powder good and uniform in 
quality. 
Considerable difficulties have been experienced, both at 
Waltham Abbey and by the merchants, in keeping the 
powder up to the specification; this might be reasonably 
expected in the production of a newarticle. The Committee 
consider themselves justified in saying that the progress 
made is encouraging, most of the difficulties having been 
overcome. Valuable knowledge is daily acquired, and light 
thrown on many points by the system of proof adopted on 
their recommendation. 
V. Another explosive picric powder consists of only two 
ingredients, saltpetre and picrate of ammonia, the in- 
gredients being incorporated in the same way as those of 
gunpowder. 
The perfect stability of the two ingredients, per se, even if 
exposed to degrees of heat very far beyond the extremes of 
tropical temperatures, has long been fully established. 
Picric powder is certainly not more susceptible of explo- 
sion by fri¢étion or percussion than gunpowder. 
Its exploding point has been compared in several ways 
with that of gunpowder. In some instances the picric 
powder exploded at a somewhat lower temperature, or 
a little more readily, than gunpowder ; in others the reverse 
was the case. The two substances may, therefore, be con- 
sidered to have about the same exploding point. 
Samples of picric powder, prepared early in 1870, which 
have been exposed to light and preserved at ordinary atmo- 
spheric temperatures, are perfectly unchanged. 
