432 
MINUTES OF PROCEEDINGS OF 
pressures may vary very irregularly and very greatly during this part of 
the action, it will be seen that the difficulty of tracing it must be very great. 
The difficulty of determining the pressure by the chronoscope, during the 
initial stages, is still further increased by the fact that the shot has to move 
some distance before shearing the first wire, and that no record of time can 
be obtained between the first moving of the shot and the shearing of the 
first wire. Any error in assuming the space through which the shot has 
moved or the velocity it has acquired when passing the first wire, must 
affect the calculation of the pressure afterwards, up to the point at least 
where the maximum occurs. 
In addition, any uncertain action of the cutters or deflexion of the sparks, 
might be sufficient to throw it out, and would not readily be detected because 
the velocity would be the same at any point, provided the area below the 
curve of pressure were the same up to that point. There would, however, 
be a difference in the total time; but, as has been noticed, the chronoscope 
does not note the time from the first starting of the shot, where the differ¬ 
ence mainly arises. 
It will be seen by reference to the pressure curves with the 8-inch gun, 
how closely the pebble curve would approximate to that of the prismatic, 
were the density increased so as to make the combustion slower at the 
commencement, and if this increase of density had also the effect of making 
the ignition more perfect, and the combustion afterwards more rapid. 
Density is considered by some as the most, if not the only important 
element to be considered in the manufacture of powder for very heavy guns. 
Drom a consideration of the various principles I have brought forward, I 
was quite prepared for the manifestation of some very high pressures in the 
proof of the 35-ton gun. I am indebted to Colonel Miller* for the following 
particulars of pressures obtained by crushers in the base of the shot» 
Charge . 75 100 110 120 130 lbs. 
Pressure . 17 25-4 31-8 46-3 63*7 tons. 
Velocity . 1163 1237 1303 1364 1348 f.s. 
Length of cartridge . 22 27§ 30 32| 35 ins. 
As the crushers in the base of the shot do not usually correspond in their 
indications with those of any crusher in the gun, a crusher plug was substi¬ 
tuted for the vent and the charge fired by electricity. The following results 
were obtained when the powder was the service pebble, and the tube in the 
service position of vent:— 
Charge. Velocity. Vent crusher. Shot crusher. 
120 1300 28-6 40-4 
120 1357 20 21*7 
Colonel Miller considers from these indications that a powder which will 
give in charges up to 80 or 90 lbs. a pressure evenly distributed over the 
powder chamber, is liable to give severe local pressures in such charges as 
were used with the 3 5-ton gun. Now the point yet to be determined is 
how far we can afford to disregard these pressures; for unless we can dis- 
# One of the Committee on Explosives. 
