NOTES FROM THE U. S. BUREAU OF MINES *
SENSITIVENESS OF EXPLOSIVES TO FRICTIONAL IMPACT.
By S. P. Howell.
~IAI;Y commercial explosives may be exploded by severe and prolonged friction, some being more sensitive than others in this regard. Explosives containing potassium chlorate are especially likely to explode under such conditions. Tests to determine sen- sitivity to frictional impact having previously been made by un- satisfactory equipment, a pendulum friction device, described in Technical Paper 234, Bureau of Mines, that permits uniformity of execution, was designed and built. The results of tests with this device on a large number of explosives and under varied con- ditions are given in the publication noted above. They indicate that the tests are not too severe, since potassium chlorate ex- plosives which failed to pass the test exploded prematurely in commercial use; all explosives of this type being extremely sensi- tive to frictional impact. Those potassium chlorate explosives that passed the tests were rendered sufficiently insensitive to fric- tion by adding an adequate quantity of mineral oil, vegetable oils, and aromatic nitro compounds, or by reducing the potassium chlorate to a small percentage. The sensitiveness of such explosives to friction is greatly increased by the presence of pyrite- bearing coal. Black blasting and ignition powders, blasting gel- atin, ammonia dynamites, and organic nitrate explosives are not as sensitive to friction impact as the nitro-glycerin and gela- tin dynamites.
APPROXIMATE QUANTITATIVE MICROSCOPY OF POWDERED ORES.
By Will H. Coghill and J. P. Bonardi.
TN ascertaining the physical and chemical properties of any given ore preparatory to prescribing the best method for its con- cemration, as many methods of gathering information as are feasible should be employed, so that all significant properties may l)e detected. Hvnes. while workinE with one of the writers sev-
* Communicated by the Director. VOL. 189. No. 1129-3
