EXPERIMENTS ON SOLID AND GASEOUS EXPLOSIVES. 371 



In ballistic tests the total energy imparted to the projectile is calculated from the 

 readings of the Holden-Boulanger chronograph, and, in the case of specially 

 constructed experimental guns, the Noble chronograph gives valuable information on 

 the distribution of pressure within the gun itself.* 



With regard to the more destructive explosives, such as blasting powders, 

 dynamite, &c., their power is usually estimated by means of the Trauzlf lead block. 

 At Woolwich this method has, however, been recently abandoned, an apparatus of 

 the pendulum type being now in use.J 



By the above methods the maximum pressure and the rate of fell of the pressure, 

 or at least the total energy, can in most cases be satisfactorily estimated. 



Comparatively little information is, however, available with regard to the initial 

 part of the explosion; i.e., the behaviour of the explosive from the moment at which 

 it is fired up to the time when it is fully consumed. 



This point deserves further investigation, the action of the explosive during this 

 period being no less important than the question of the maximum pressure attained. 



It must be borne in mind that any structure, whatever its nature, will behave very 

 differently according as it is exposed to a stress gradually applied, or is subjected 

 suddenly to the same stress, or finally is submitted to violent oscillations of load. 



In the case of a gun any abnormally rapid explosion gives rise also to another 

 source ot danger. The time elapsing between the ignition and the complete 

 combustion of the charge may be insufficient to allow the inertia of the shot to be 

 overcome and to move it through an appreciable distance. Should this occur, the 

 products of combustion would be confined in an unduly small space, and the pressure 

 would rise above the safe limit. 



The study of the initial stage of the explosion for various powders has formed part 

 of the researches carried out by the Service des Poudres et Salpetres in Paris. The 

 gauge first used by VIEILLE was a modification of the crusher gauge , while of late 

 years he has worked with a new type of spring manometer. || 



In Germany, BICHEL, BRUNSWIG^ and others have suggested that the properties of 

 explosives should be determined by measurements made at relatively low pressures, 

 the results being deduced by extrapolation. Careful work has been carried out by 

 BLOCHMANN** under these conditions. The gravimetric densities ft used are from O'Ol 



* 'Report Brit. Assoc.,' Oxford, 1894, pp. 523-540. 



t 'Ber. Int. Kong. Angew. Chem.,' Berlin, 1903, vol. II., pp. 299-303 and 462-465. 

 I Captain DESBOROUGH'S report. See '25th Report of H.M. Inspector of Explosives.' 

 'Comptes Rendus,' vol. 112, p. 1052, 1891. 



|| ' Memorial des Poudres et Salpetres,' vol. XL, pp. 157-210, 1902 ; see also ' Comptes Rendus,' vol. 115, 

 p. 1268, 1892. 



H 'Ber. Int. Kong. Angew. Chemie,' vol. II., pj. 282-299, 1903. 

 ** 'DiNGLER's Poly. Journ.,' vol. 318, pp. 216 ar.d 332, 1903. 



tt Gravimetric density is defined as the ratio of the weight of the charge to the weight of that volume 

 of water which would fill the enclosure ; it is, therefore, numerically equal to the specific gravity of the gas 

 produced when the explosive is fired. 



3 B 2 



