SHORT NOTES ON PROFESSIONAL SUBJECTS. 
125 
76. 
The following is an abstract of the recent preliminary report by the Committee 
on Explosives, 5. 2. *70 
In the Memorandum of Instructions furnished to the committee, their attention 
was specially directed to " the importance of an early determination of the description 
of gunpowder whose employment in large charges is attended with the least risk of 
over-straining the guns, 55 and they were desired to report progress from time to 
time on this part of the question. 
The committee have, therefore, up to the present time, given their attention 
specially, and almost exclusively, to this branch of the enquiry entrusted to them. 
They consider that sufficient progress has now been made in the experiments 
bearing upon this subject which have been carried on with the 8-inch M.L. gun, 
to show that there is no difficulty in producing a description of powder much 
better suited for use in guns of large calibre than the present service powders. 
In investigating the action in the gun of the above descriptions of gunpowder, 
the committee have availed themselves of the following means, namely :—* 
a. The determination of the time a projectile takes to traverse various intervals 
within the bore of a gun. This was accomplished by means of a chronoscope 
designed to measure very small intervals of time. 
b. The determination of the pressure, directly, by means of Rodman’s 
pressure gauge, fitted on the exterior of the gun and communicating with the 
interior of the bore by means of a hollow screw plug. 
c. The determination of the pressure, directly, by means of a new form of 
inner gauge, termed a “ crusher, 55 designed expressly for the committee. 
With a view of investigating the influences exerted by the chemical and physical 
characters of the different descriptions of gunpowder, upon the results furnished 
by them as regards velocity and pressure, each variety has been submitted to 
complete analysis and to a determination of density by means of the mercury- 
densimeter. 
The Chronoscope. —The principle of action of this instrument consists in regis¬ 
tering, by means of electric currents upon a recording surface travelling at a 
uniform and very high speed, the precise instant at which a shot passes certain 
defined points in the bore. 
It consists of two portions; firstly, the mechanical arrangement for obtaining 
the necessary speed, and keeping that speed uniform; secondly, the electrical 
recording arrangement. 
The “ Rodman 55 Pressure Gauge.” —This gauge is so well known that the 
committee have considered it unnecessary to do more than give a very brief 
description of it. 
The extreme variability of the results given with this instrument led them to 
devise a modified form of the pressure gauge, in which some of the causes of error 
inherent in the “Rodman 55 gauge were eliminated. 
The “ Crusher 55 Gauge. —This apparatus was made in the Royal Gun Factories 
at the suggestion of the committee. It consists of a screw plug of steel, provided 
with a movable base which admits of the insertion of a small copper cylinder in a 
chamber. One end of this cylinder rests on an anvil, while the other is acted 
upon by a movable piston, which is kept tightly against the cylinder by means of 
a spring. The cylinder is centred in the chamber by a small watch spring. 
17 
