METHODS OF TESTING EXPLOSIVES MUNEOE. 305 



(T) where a sharp line is formed by the effects of the detonation itself, and 

 the lead is often broken through at this point. The distance from (M) to (T) 

 is accurately measured and designated as (&). If the two ends of the fuse are 

 detonated simultaneously (M) and (T) fall together; that is, the detonation pro- 

 ceeds at the same rate through the two halves of the fuse and meets at the mid- 

 dle, but when a certain length of an explosive is placed in the circuit we have 

 on one side one-half the length of the fuse and on the other side one-half the 

 length of the fuse plus a certain measured length of explosive. We have thus, 

 letting — • 



X=Velocity of detonation of the explosive tested. 



V=Known velocity of the fuse (6,000 meters per second). 



A=Distance between two ends of fuse, or length of explosive tested. 

 6=Distance between M and T. 

 Then,— 



^_VA 6000A 

 26 2b • 



As to the accuracy of the test, it was found that by using the fuse alone (M) 

 and (T) always coincided to within one-eighth of an inch (3 millimeters). It 

 is easily seen that errors in measurement will be diminished by increase in 

 the length of explosive tested, and it can be calculated, with velocities of 4,000 

 to 6,000 meters per second, using 15 inches (38 centimeters) of powder, that 

 an error of one-fourth of an inch (6 millimeters) in measurement of the dis- 

 tance (M) to (T), which is a very large one under the conditions, introduces an 

 error in the determination of the velocity of about 5 per cent. 



Comey and his associates have tested this method quite fully at 

 the eastern laboratory of the Du Pont Powder Co., and have found 

 that it gives not only a ready and accurate means of determining the 

 velocity of detonation through a column of any desired length of 

 explosive, but that it is also possible by this method to determine 

 the velocity with which a detonation wave travels through the air. 



Tt is obvious that the fiame-giving qualities of an explosive plays 

 a most important part in its liability to ig-nite fire damp and other 

 combustible mixtures, and that, all other conditions being equal, that 

 explosive which gives the shortest flame for the briefest time is most 

 suitable for use. Hence latterly much attention has been given to 

 the study of the flames from explosives, and many devices have been 

 constructed by which to photograph them. 



Among these is the one employed at the Pittsburg testing station, 

 where the flame is photographed on a moving film. The charge of 

 explosive is fired from a " cannon " of the type used in the gallery 

 tests by means of an electric detonator or ig-niter, but in this test 

 the " cannon " is mounted vertically in a concrete foundation at a 

 distance of about 18 feet from the lens of the camera. To cut off 

 extraneous light rays, so that the tests may be made at any time, 

 the " cannon " is inclosed in an iron cylinder 20 feet in height and 

 43 inches in diameter, which is connected with the dark room by a 

 light-tight iron conduit, as shown in plate 11. The cylinder, or 



97578°— SM 1910 20 



