538 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



The relative strength of detonators is determined by the sand 

 test as perfected by the bureau. 



TESTS OF DETONATORS AND ELECTRIC DETONATORS. 



The Bureau of Mines not only tests explosives to determme their 

 permissibility, but also prescribes the conditions under which they 

 are to be used. One of these conditions is that permissible explosives 

 shall be fired by a detonator, preferably an electric detonator, hav- 

 ing a charge equivalent to that of the standard detonator used at the 

 bureau's Pittsburgh experiment station. The gi'ade of electric de- 

 tonator is recommended by the manufacturer for use with a par- 

 ticular brand of permissible explosive; and should the explosive pass 

 the required tests with the gi\Tde recommended, the same grade is 

 prescribed by the bureau, but in no case can it be of less efficiency 

 than a No. 6 electric detonator. A further requirement is that the 

 charge of the detonator or electric detonator shall consist by weight 

 of 90 parts of mercury fulminate and 10 parts of potassium chlorate 

 or tlieir equivalents. 



The importance of these prescribed conditions may be realized 

 by considering the means whereby permissible explosives are fired 

 in practice. Detonators or electric detonators are required for firing 

 all permissible explosives now on the bureau's list. Although the 

 explosives might, in many cases, be partly exploded by the aid of 

 squibs or fuse or by means of black-powder primers, yet the ex- 

 plosion so produced would not be complete ; the explosives would not 

 be used to their best advantage, and the gases produced would 

 usually be dangerous. Therefore it is safer to fire detonating ex- 

 plosives with detonators or electric detonators strong enough to 

 cause complete detonation. 



The results of experiments made by the bureau show that the 

 average percentage of explosives failing to detonate was increased 

 more than 20 per cent when the lower grades of electric detonators 

 were used instead of No. 6 electric detonators and was increased more 

 than 50 per cent when these lower grades were used instead of No. 8 

 electric detonators. 



DEVELOPMENT OF SAFER MINE ELECTRICAL EQUIPMENT. 



For several years past the bureau has been working to bring about 

 the retirement from mines of dangerous open-flame lamps and the 

 substitution of the relatively safe electric lamp operated by a battery 

 carried on the miner's belt. 



The individual electric lamp, if generally adopted, will be a long 

 step toward safety, as it cannot start fires or explosions as open-flame 

 lamps may. Moreover, electric lamps give more light and distribute 



