Compressed Air Work And Diving 1909

EXPLOSIVES. 99 clown the scale. The absorbing material is a specially preparecl form of gun-cotton which is itself a high cxplosive, so that biasting’ gelatine has practically the strength of pure nitro-glycerine. The absorbing pre paration is about 7 per cent, and the pure absorbed nitro-glycerine 93 per cent. It is very suitable for use under water, as it can be left there under ordinary conditions for a long time without deterioration in power. It is suitable for hard rock rather than soft, and should not be used where it is desired to detach Lir^c slabs without injury. Its property is to shatter rather than to move, Nobels gelignite contains about 62 per cent, of nitro-glycerine, the other materials being nitro-cotton, nitrate of potash, and woodmeal. From this it will be seen it is not so powerful as biasting gelatine. It is rather slower in exploding’, and therefore less intense in local action. It will not resist water so well cis bla.stin°' gelatine. Gelatine dynamite is intermediate in character between biasting gelatine and gelignite as reoards strength and water-resisting properties. The compara- tive strengths of these four explosives, taking dynamite as 100, are biasting gelatine, 150; gelatine dynamite, 130; gelignite, 110.* There are a large number of other explosives on the malket which differ only in the nature of the absorbent and percentage of nitro-glycerine. F01 rock biasting in tunnel and caisson work it will not be economical to use explosives with too low a percentage of nitro-glycerine. As a general rule the inert material should not exceed 25 per cent., as in Book ol High Explosives,” Nobel’s Explosives Co.