296 ANNUAL EEPOKT SMITHSONIAN INSTITUTION, 1910. 



Firing trials with the standard show that variables enter here, and 

 that the same pendulum deflection is not invariably obtained with 

 equal weights of charge of the standard dynamite, even though the 

 successive charges are tamped in the " cannon " with the same degree 

 of pressure, stemmed with the same weight of fire clay, and fired by 

 the same numbered detonator. A condition affecting this result is 

 the distance of the " cannon " from the mortar, and hence, as shown 

 above, this distance has been definitely fixed. Another is the posi- 

 tion of the knife-edges supporting the pendulum mortar, and to 

 eliminate the effect of this the knife-edges are trammeled before each 

 trial. Other factors affecting the results are the direction and 

 velocity of the wind, the condition of the bore hole in the " cannon," 

 and that of the person charging the " cannon." No one of these can 

 be controlled absolutely. Hence, the explosive to be tested must be 

 proved in this ballistic-pendulum test directly against the standard, 

 both being handled and charged by the same person on the same day 

 and as nearly as possible under the same conditions, for this tends to 

 eliminate the personal equation, through its effects becoming nearly 

 uniform, and to eliminate the effects of wind and weather, since they 

 are fairly miiform during the trial periods. The condition of the 

 bore hole is the existing variable factor which is the most difficult of 

 elimination. 



The energy of the explosive is further ascertained comparatively 

 by the Trauzl and by the small lead-block tests. The device used in 

 the Trauzl test is shown in plate 6, which consists of lead blocks 200 

 millimeters in diameter and 200 millimeters in height, in which holes 

 25 millimeters in diameter and 125 millimeters in depth are bored 

 centrally in the top. These cylinders are cast from desilvered lead 

 and all used in the same series of tests are carefully prepared under 

 identical conditions and from the same melt. The volumes of these 

 bore holes are carefully measured by means of water. 



Ten grams of the explosive, weighed on a balance of precision, are 

 wrapped in similar-sized pieces of tin foil, together with a No. 7 elec- 

 tric detonator, and the whole inserted in the bore hole of one of these 

 cylinders, then 40 cubic centimeters of dry Michigan dune sand, of 

 such fineness that it will all pass through a 50-mesh screen and be 

 caught on an 80-mesh one, are poured into the bore hole and tamped 

 10 blows with an automatic tamping device, which operates on the 

 principle of an automatic center punch, and delivers blows of known 

 magnitude over a definite area. Then 10 cubic centimeters more of 

 the same sand are poured in and tamped with 40 blows of the tamp- 

 ing device. The loaded cylinder is placed on a piece of heavy shaft- 

 ing imbedded in concrete, which forms a rigid support, the tempera- 

 ture of the block is ascertained to make sure that it is 15° C, and, 

 when this is attained, the charge is fired. The cavity is again meas- 



