METHODS OF TESTING EXPLOSIVES MTJNEOE. 299 



on its seat by springs of known dimensions and effect. A stylus is 

 mounted on the upper end of the stem of the piston in such manner 

 that it moves freely only in the vertical plane, while the motor-driven 

 drum at its rear, against which it impinges, rotates horizontally, 

 thus producing a curve which, by its magnitudes and variations, 

 records the extent of the pressures developed from the beginning to 

 the end of the explosion. 



The charge of explosive used varies from 100 to 200 grams, ac- 

 cording to its character, as judged by the results of the chemical 

 analysis which has been made of it. The explosive is removed from 

 its original wrapper and inclosed in a wrapper of tinfoil in such 

 manner as to preserve its original density. The head of the cylinder 

 is removed, the No. 7 electric detonator passed through the glanded 

 plug, and then inserted and secured in the cartridge, the fused car- 

 tridge laid on a small wire support in the center of the cylinder, the 

 head replaced, the vacuum produced, the indicator drum set in revo- 

 lution, and then, all parts being found secure and operative, the 

 charge is fired and the indicator diagram taken. Three shots are 

 made with each of the different cooling surfaces. 



After the explosion the products are allowed to cool to the room 

 temperature which, with the tension of the gases, the barometer and 

 the volume of the cylinder, is noted and the volume of the gaseous 

 and vaporous products is reduced to normal. A sample of these 

 gases and vapors is then drawn out through the exhaust opening and 

 analyzed. The liquid and solid products are recovered, measured, 

 and analyzed after the head has been removed. 



As is well recognized, the heat developed by an explosive when 

 it explodes is one of the most important of the factors which deter- 

 mine its effect, and since Berthelot first employed the calorimetric 

 bomb with which to directly measure the number of heat units set 

 free by a known weight of an explosive, attention has been given to 

 the improvement of this device so as to render it more useful. One 

 of the modern forms of this instrument is Mettegang's explosion 

 calorimeter, which is shown in plate 8. 



This consists of a bottle-shaped calorimetric bomb 30 inches high, 

 with a capacity of 30 liters, made of wrought steel one-half inch in 

 thickness, and closed by a cap having an air-tight fit. Two holes are 

 tapped into this bomb on opposite sides of the curvature of the 

 neck, into one of which a valve is tapped by which to connect the 

 bomb with an air pump, and into the other a plug through which 

 the legs of the detonator are carried. This bomb when charged is 

 placed in an immersion vessel, filled with a known weight of water, 

 which is made of nickel-plated copper one-sixteenth inch in thick- 

 ness, and which is strengthened by bands of copper wire wound about 

 the outside. The immersion vessel is placed, with its contained 



