[Footnote A:  Berthelot, “Explosives and their Power.”]

The “explosive wave” (of Berthelot) for dynamite is about 5,000 metres per second.  At this rate the explosion of a cartridge a foot long would only occupy 1/24000 part of a second, while a ton of dynamite cartridges about 7/8 diameter, laid end to end, and measuring one mile in length, would be exploded in one-quarter of a second by detonating a cartridge at either end.[A] Mr C. Napier Hake, F.I.C., the Inspector of Explosives for the Victorian Government, in his paper, “Notes on Explosives,” says:  “The theoretical efficiency of an explosive cannot in practice be realised in useful work for several reasons, as for instance in blasting rock—­

“1.  Incomplete combustion.

“2.  Compression and chemical changes induced in surrounding material.

“3.  Energy expended in cracking and heating of the material which is not displaced.

“4.  The escape of gas through the blast-hole and the fissures caused by the explosion.

“The useful work consists partly in displacing the shattered masses.  The proportion of useful work obtainable has been variously estimated at from 14 to 33 per cent. of the theoretical maximum potential.”

[Footnote A:  C.N.  Hake, “Notes on Explosives,” Jour.  Soc.  Chem.  Ind., 1889.]

Among the various forms of dynamite that are manufactured is carbo-dynamite, the invention of Messrs Walter F. Reid and W.D.  Borland.  The base is nitro-glycerine, and the absorbent is carbon in the form of burnt cork.  It is as cheap as ordinary dynamite, and has greater explosive force, seeing that 90 per cent. of the mixture is pure nitro-glycerine, and the absorbent itself is highly combustible.  It is also claimed that if this dynamite becomes wet, no exudation takes place.

Atlas powder is a dynamite, chiefly manufactured in America at the Repanno Chemical Works, Philadelphia.  It is a composition of nitro-glycerine, wood-pulp, nitrate of soda, and carbonate of magnesia.  This was the explosive used in the outrages committed in London, by the so-called “dynamiters.”  Different varieties contain from 20 to 75 per cent. of nitro-glycerine.

The Rhenish dynamite, considerably used in the mines of Cornwall, is composed of 70 parts of a solution of 2 to 3 per cent. of naphthalene in nitro-glycerine, 3 parts of chalk, 7 parts of sulphate of barium, and 20 of kieselguhr.

Kieselguhr dynamites are being largely given up in favour of gelatine explosives.  The late Colonel Cundill, in his “Dictionary of Explosives,” gives a list of about 125 kinds of dynamites.  Many of these, however, are not manufactured.  Among the best known after the ordinary No. 1 dynamite are forcite, ammonia dynamite, litho-fracteur, rendock, Atlas powder, giant powder, and the various explosive gelatines.  They all contain nitro-glycerine, mixed with a variety of other substances, such as absorbent earths, wood-pulp, nitro-cotton, carbon in some form or other, nitro-benzol, paraffin, sulphur, nitrates, or chlorates, &c. &c.