1907.] on Fifty Years of Explosives. 459 



determining changes of temperature, not absolute values. They 

 could be read approximately to 0''001 C. 



Generally two observations were sufficient to determine the heat 

 units. Thus, in the explosive which showed the least variation in 

 tranformation, ItaUan BaUistite, lowest heats were 1308-9 and 

 1293-5; mean, 1301*2 units. Highest heat, 1340-6, 1329-9; 

 mean, 1335-3. 



Norwegian, Lot 165. Lowest, 925*1 and 9ul-4 ; mean, 913-3. 

 Hidiest, 1099-9 and 1102-3; mean, 

 ^^ 1101-1. 

 Norwegian, Lot 167. Lowest, 994-7 and 986*1 ; mean, 990-4. 

 Hidiest, 1136-7 and 1142-1; mean, 

 " 1139-4. 



The last apparatus with which I shall trouble you is that 

 employed for determining the time that explosives of various forms 

 and natures require for their transformation, and also for deter- 

 mining the rate at which the gases communicate their heat to the 

 ■walls of the vessel in which they are confined. 



The apparatus, which I show on the screen, consists of the usual 

 explosion vessel, closed at the two ends by gas-tight plugs, through 

 one of which passes the firing wire, while at the other end is fitted a 

 pressure indicator provided with a steel plunger of small area, which 

 is exposed to the gas pressure. An enlarged continuation of this 

 plunger engages the end of a spiral spring, the strength of which has 

 been accurately determined. Attached to the plunger at B is a lever, 

 the fulcrum of which is fixed to the stationary bracket of the indica- 

 tor, so that when the spring is compressed, motion is given to the 

 end of the lever. 



Fixed to the lever are two electric magnets, D — one to record 

 seconds, the other to complete the firing circuit. A rocking bar, E, 

 is coupled up over the seconds magnet, which is again coupled at the 

 other end by a link, F, thus conveying the seconds beats of the 

 •chronometer to the pen tracing its path on the revolving drum. 



Fixed to the frame of the revolving drum are two rods, G G, 

 upon which slide the carriage , carrying the recording pen. The pen 

 is not in contact with the drum, being held up by a detent which is 

 ■only liberated by the current which fires the charge. 



It is necessary to have two speeds to the drum — one very rapid, 

 about forty inches to a second ; the other very slow, about one inch 

 per second. 



Before firing, the fast speed is employed, the slow speed band 

 running free. Between one and two seconds after firing the change 

 speed lever is raised, thus releasing the fast and employing the slow 

 motion. The diagram is traced on a sheet of tinfoil backed by paper. 



The chronometer is of the ordinary marine type, but is furnished 

 'with a seconds make and break arransrement. 



