strong fulminate detonator.  The direct contact of water disintegrates dynamite, separating the nitro-glycerine, hence great caution is necessary in using it in wet places.  It freezes at about 40 deg.  Fahr. (4 deg.  C.), and remains frozen at temperatures considerably exceeding that point.  When frozen, it is comparatively useless as an explosive agent, and must be thawed with care.  This is best done by placing the cartridges in a warming pan, which consists of a tin can, with double sides and bottom, into which hot water (130 deg.  Fahr.) can be poured.  The dynamite will require to be left in for some considerable time before it becomes soft.  On no account must it be placed on a hot stove or near a fire, as many serious accidents have occurred in this way.

Frozen dynamite is a hard mass, with altered properties, and requires 1.5 grm. of fulminate instead of 0.5 grm. to explode it.  Thawing may also cause exudation of the nitro-glycerine, which is much more sensitive to shock, and if accidentally struck with an iron tool, may explode.  It is a dangerous thing to cut a frozen cartridge with a knife.  Ramming is even more dangerous; in fact it is not only dangerous, but wasteful, to use dynamite when in a frozen state.

Dynamite explodes at a temperature of 360 deg.  Fahr., and is very sensitive to friction when hot.  In hot countries it should never be exposed to the rays of the sun.  It should, however, not be kept in a damp or moist place, as this is liable to cause exudation.  Sunlight, if direct, can cause a slow decomposition, as with all nitro and nitric compounds.  Electric sparks ignite, without exploding it, at least when operating in the open air.

Dynamite, when made with neutral nitro-glycerine, appears to keep indefinitely.  Sodium or calcium carbonate to the extent of 1 per cent. is often added to dynamite to ensure its being neutral.  If it has commenced to undergo change, however, it rapidly becomes acid, and sometimes explodes spontaneously, especially if contained in resisting envelopes.  Nevertheless, neutral and well-made dynamite has been kept for years in a magazine without loss of its explosive force.  If water is brought into contact with it, the nitro-glycerine is gradually displaced from the silica (guhr).  This action tends to render all wet dynamite dangerous.

It has been observed that a dynamite made with wood sawdust can be moistened and then dried without marked alteration, and from 15 to 20 per cent. of water may be added to cellulose dynamite without depriving it of the power of exploding by strong detonator (this is similar to wet gun-cotton).  It is, however, rendered much less sensitive to shock.  With regard to the power of No. 1 dynamite, experiments made in lead cylinders give the relative value of No. 1 dynamite, 1.0; blasting gelatine, 1.4; and nitro-glycerine, 1.4.  The heat liberated by the sudden explosion of dynamite is the same as its heat of combustion,[A] and proportionate to the weight of nitro-glycerine contained in the mixture.  The gases formed are carbonic acid, water, nitrogen, and oxygen.