266 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1908. 



Further progress, although seemingly small, has been that made 

 in joowder for safety fuses. Formerly it was not uncommon to use 

 the siftings from mining powder for safety fuses, but the present 

 stringent requirements have compelled all manufacturers to make 

 a special quality of fuse powder of constant composition, density, 

 and uniformity of granulation, in spite of its almost dustlike char- 

 acter. 



I shall lay before you later on some information concerning safety 

 explosives for fiery mines, and, therefore, will only mention that in 

 every European country the use of gunpowder is prohibited in such 

 workings. Considerable surprise was therefore felt when several 

 black-powder-like mixtures passed the official test for permitted ex- 

 plosives in this country. Later, when these tests were made more 

 rigorous, these explosives disappeared, but one of them, bobbinite, 

 passed even the more stringent tests, and is still on the new list of 

 permitted explosives. 



Complaints having been made as to the alleged danger of bobbinite 

 in fiery mines, the home office appointed a departmental committee 

 in 190G to investigate the matter, which came to the conclusion that 

 the use of bobbinite should not for the present be restricted.'^ The 

 importance of this explosive may be gauged from the fact that over 

 a million pounds of bobbinite were used in 1907 in this country. 



With regard to machinery used in the manufacture of black powder 

 and similar mixtures there has, of course, been very little improve- 

 ment. Mixing, granulating, and glazing are still carried out in the 

 same way, and for the purpose which they have to accomplish the 

 machines do all that can be desired. A good deal of ebonite was 

 formerly used in connection with machinery for black powder, such 

 as for plates in cake presses, for lining the hoppers of cutting ma- 

 chines, etc. In cake presses there are alternate layers of powder 

 containing sulphur, and of highly insulating ebonite, which remain 

 together under pressure for some time. It is a rule in explosives 

 works that at the approach of a thunderstorm the workers leave their 

 houses, and it is frequently found convenient, meanwhile, to leave the 

 charge under pressure. This would practically constitute an electric 

 pile, and as a matter of fact several explosions have occurred when, 

 after the thunderstorm, the workers opened the presses. In one in- 

 stance, at least, the fact of a long spark having come out of the charge 

 could be elicited from the attendant before his death. 



Following a suggestion made by the author twenty years ago, a 

 number of factories have substituted plates of fiber for these ebonite 

 plates with great success. 



<* Report of the Departmental Committee on Bobbinite. London, 1007. 



