May 



900] 



NA TURE 



lime required for the combustion of charges of cordite in which 

 the cordite was of different thicknesses, varying from o 05 inch 

 to o-6o of an inch ; (2) the rapidity with which the explosives 

 part with their heat to the vessel in which the charge is con- 

 fined ; and (3) to ascertain, if possible, by direct measurement, 

 the temperature of explosion, and to determine the relation 

 l)etween the pressure and temperature at pressures approxim- 

 ating to those which exist in the bore of a gun, and which are, 

 of course, greatly above any which have yet been determined. 



As reganls the first two objects I have named, I have had no 

 serious difficulties to contend with, but as regards the third, I 

 have so far had no satisfactory results, having been unable to 

 use Sir W. Roberts Austen's beautiful instrument owing to the 

 temperature at the mpnient of explosion being greatly too high, 

 high enough indeed to melt and volatilise the wires. 



I am, however, endeavouring to make an arrangement by 

 which I hope to be able to determine these points when the 

 temperature is so far reduced that the wires will no longer be 

 fused. 



If the piston be left free to move the instant of the commence- 

 ment of pressure, the outside limit of the time of complete ex- 

 plosion will be indicated ; but, on account of the inertia of the 

 moving parts, the pressure indicated will be in excess of the 

 true pressure, and the excess will be, more or less, inversely as 

 the time occupied by the explosion. 



If we desire to know the true pressure, it is necessary to com- 

 press the gauge beforehand to a point closely approximating to 

 the expected pressure, so that the inertia of the moving parts 

 may be as small as possilile — the arrangement by which this is 

 effected is not shown in the photograph, but the gauge is retained 

 at the desired pressure by a wedge-shaped stop, held in its place 

 by the pressure of the spring, and to the stop a heavy weight is 

 attached — when the pressure is relieved by the explosion, the 

 weight falls and leaves the spring free to act. 



I have made a large number of experiments with this instru- 

 ment, both with a variety of explosives and with explosives fired 

 under different conditions. Time will not permit me to do more 

 than to show you on the screen three pairs of experiments to 



The apparatus I have used for these experiments is placed on 

 he table. The cylinder in which the explosives were made 

 :- too heavy to transport here, but this photograph (Fig. 8) will 

 sufficiently explain the arrangement. The charge I used is a little 

 more than a kilogramme, and it is fired in this cylinder in the 

 usual manner. 



The tension of the gas acting on the piston compresses the 

 >pring, and indicates the pressure on the scale here shown. But 

 o obtain a permanent record, the apparatus I have mentioned is 

 employed. 



There is, you see, a drum made to rotate by means of a 

 small motor. Its rate of rotation is given by a chronometer 

 acting on a relay, and marking seconds on the drum, while the 

 magnitude of the pressure is registered by this pencil actuated by 

 he pressure-gauge I have just described. 



To obtain with sufficient accuracy the maximum pressure, and 

 also the time taken to gasify the explosive, two observations — 

 that is, two explosions — are necessary. 



NO. 1596, VOL. 62] 



illustrate the effect of exploding cordite of different dimensions, 

 but of precisely the same composition. 



I shall commence with rifle cordite. In this diagram (Fig. 9) 

 the axis of abscissae has the time in seconds marked upon it, 

 while the ordinates denote the pressures, and I draw your atten- 

 tion to the great difference, in the initial stage, between the red 

 and the blue curves. You will notice that the red curves show a 

 maximum pressure some 4.^ tons higher than that shown by the 

 blue curve ; but this pressure is not real. It is due to the 

 inertia of the moving parts. The red and blue curves in a very 

 small fraction of a second come together, and remain practically 

 together for the rest of their course. The whole of the charge 

 is consumed in something less than fifteen thousandths ("015) 

 of a second. 



In the case of the blue curve the maximum pressure indicated 

 is obtained in the way I have described, and is approximately cor- 

 rect— about nine tons per square inch. The rapidity with which 

 this considerable charge parts with its heat by communication to 



