THE CRUSHER GAUGE. 23 



which is fixed on the plug, and the other on a central metallic 

 rod, n, which traverses the plug, from which it is isolated through 

 the interposition of a thin coating of shellac. The crusher, as is 

 well known, was proposed and applied in 1871 in England by 

 Captain Noble, in his researches on the combustion of powder. 

 It is fitted to the plug, B', and consists of a piston, a, of tempered 

 steel, easily fitting in a channel following the axis of the plug, 

 and of a cylinder of copper, r, 0-008 metres in diameter and 

 0*013 metres in height, placed between the piston-head and 

 stopper screwed into the plug. 



6. In the method of calibration adopted by the naval artillery, 

 the cylinders are crushed under weights acting without initial 

 velocity, and the reduced heights of the crushed cylinders are 

 measured. From this, by interpolation, is derived a table 

 establishing empirical relations between these heights h, called 

 remaining heights, and the corresponding weights, R. Taking IT 

 to represent the maximum pressure developed in an experiment, 

 and w the area of the base of the piston, TT is calculated by the 

 ratio TTW = E. In order to keep the pressure within the limits 

 of the testing table, it is sufficient to vary the base of the piston. 



The results obtained are compared by introducing into the 

 same chamber increasing weights of the explosive substance. 

 The ratio of the weight of the explosive to the internal volume 

 of the eprouvette, is termed the density of charge (see p. 28). 



7. The theory of crushing manometers, such as the crusher 

 above described, has been examined in a most thorough manner 

 by Sarrau and Vieille. 1 They first calibrated the apparatus by 

 crushing the cylinder progressively and slowly by very small 

 amounts, until it supported without permanent deformation a 

 given charge. From this was obtained a ratio between the 

 final charge, called the force of calibration (force de tarage), 9 and 

 the diminution in the height of the cylinder, that is, the corre- 

 sponding crushing E. K and K being constants independent of 

 the explosive, varying from 1000 kgms. to 3500 kgms., we 

 have 



(1) = K + K : K = 541 : K = 535, 



the units being the millimetre and kilogramme. 



This relation being established, how can the resulting indica- 

 tion be applied to experiments ? Two limiting cases present 

 themselves : 



(a) The development of the pressure is slow enough, and the 

 mass of the crushing piston small enough, to permit of the 

 forces of inertia being neglected ; in this case there is practically 

 equilibrium between the pressure developed by the explosion 

 and the resistance of the cylinder. The maximum pressure is 



1 u Comptes rendus des stances de 1'Academie des Sciences," pp. 26, 130, 

 et 180. 1882. 



