METHODS OF TESTING EXPLOSIVES MUNEOE. 297 



ured by calibration with water and the increase in vohime produced 

 by the charge of explosive fired is compared with that produced by 

 an equal weight of the standard dynamite fired under the, same con- 

 ditions. The Trauzl test is quite widely used, and abroad it has been 

 recommended that the cylinder be covered by a lead plate secured by 

 a yoke. But it is found that in putting on the yoke the charge and 

 stemming were disturbed and, as uniformity in these last particulars 

 are of much more impoi'tance in these comparative tests than a 

 greater degree of confinement, the plate and yoke are not recom- 

 mended. 



The Trauzl test measures comparatively the displacing effect of an 

 explosive under moderate confinement. The small lead-block test 

 measures com^Daratively the pressure exerted in contact by a charge of 

 explosive which is detonated or exploded unconfined, or, in otlier 

 words, the percussive effect. The blocks used and the defonnations 

 produced on some of them are shown in plate 6, figure 2. The lead 

 blocks employed are cylinders 1^ inches in diameter and 2^ inches 

 high. The charge of explosive used is 100 grams. Since an uncon- 

 fined charge of high explosive, such as the standard dynamite, would, 

 on detonation in contact, deform the cylinder beyond measurement, 

 as shown by F in the figure, a disk of annealed steel 1^ inches in 

 diameter and one-fourth inch in thickness is placed upon the lead 

 cylinder. Since this plate retains a portion of the energy expended 

 the compressed cylinders record only the residual energy. 



In malving the test, after placing the steel disk on the cylinder, a 

 strip of manila paper is so secured about and bej^ond them as to pro- 

 vide a container, above the plate, for the explosive to be fired. The 

 cylinder is then placed on a rigid support, the carefully weighed 

 charge of explosive poured in and so tamped as to acquire the specific 

 gravity it possessed in its original container, the No. 7 electric deto- 

 nator inserted, and the charge fired. The height of the compressed 

 cylinder is then ascertained with precision, and this comparison, as 

 compared with that produced in a cylinder subjected to the detona- 

 tion of 100 grams of the standard dynamite, is styled the relative per- 

 cussive force of the exj)losive. 



A more accurate idea of the pressures produced by an explosive 

 may be obtained by means of the Bichel pressure gauge which is 

 employed to determine the " maximum pressure of an explosive in its 

 own volume," by which is meant the maximum pressure which an 

 explosive exerts when exploded or detonated in a space which it fills 

 completely, and when all of the heat set free through the chemical 

 reactions taking place during the explosion are retained by the prod- 

 ucts of the reaction. Evidently this condition never actually obtains 

 in practice, for a portion of this heat is always communicated to the 

 walls of the inclosure. The portion tluis lost from the products dif- 



