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MINUTES OF PROCEEDINGS OF 
shown, leading us to believe that this is one of the most important points 
to be taken into consideration in the manufacture of powder for very heavy 
guns. 
With slow burning powders, the Committee state, the indications of pres¬ 
sure given by the “ crushers " have been found to correspond very closely 
with those deduced from the chronoscope ;* but this is not the case with 
quick burning powders, nor even with slow burning powders when fired in 
large charges in very heavy guns. Prom Rodman's vexperience with his 
pressure gauge, we cannot doubt that the crusher is not in all cases to be 
relied on. It seems to indicate intense local pressures which are greater 
as the point of their action is more distant from the point of ignition of 
the charge, greater at the extremities of the chamber than at the point of 
ignition in the middle, and greater when the crusher is at a distance from 
the bore than when close to the bore, amounting in some cases to double 
the pressure deduced from the “ chronoscope," or even more. As an 
instance, the Committee state that, with R.L.G. in an 8-inch gun, when 
the “ crusher" was close to the bore, the pressure indicated was 22J tons, 
but when at a distance, it was 40 tons per square inch. 
The occurrence of these pressures would appear, in the estimation of the 
Committee, to correspond with the notion already mentioned as having been 
investigated by Robins, of the gas first formed being suddenly arrested 
when at a high velocity and converted as by a blow into pressure. But 
when the crushers are put in a second time, little or no further setting up 
takes place, as would be the case if the action were due to a blow produced 
by the mass of gas in motion. Under such a supposition the intense pres¬ 
sures would take place before the general maximum is attained, and it is 
difficult to conceive that the necessarily small mass of gas is sufficient to 
produce the results manifested. 
It is more reasonable to suppose that they occur at the moment when 
the general maximum exists, and may be superadded to it. In addition, it 
appears both from Rodman's experiments and those of the Committee, that 
when once the action is set up, it is continued throughout the bore, which 
would not be the case were it due to the velocities of the gases first ignited. 
This continuance of the action is also unfavourable to the supposition that 
it is due to an intense general pressure of the amount indicated, which, as 
shown by Rodman, would gradually subside as the gas expanded and pro¬ 
duce no further vibration. It might, however, be explained were the general 
pressure of the nature of water pressure, which would suddenly subside with 
a very small motion of the shot, and so produce vibration by sudden 
cessation ; and in support of this view it may be said there is a marvellous 
harmony in the fact that Rumford, Rodman, and the Committee all find 
these pressures manifesting themselves somewhere about 30 tons. 
The apparently local nature of the pressures might be accounted for by 
the relief which would be given at those points where the gas could escape, 
such as the vent and the base of the shot. The vibration, however, would 
equally be set up by a moderate general pressure if it were suddenly applied, 
* This can only refer to the chronoscopic pressures at and after the maximum. During the 
ascending branch of the curve the crushers can only show the maximum pressure. 
