tubes filled with
pulverised gun-cotton has been found to be from 5,000 to 6,000 mms. per
second in tin tubes, and 4,000 in leaden tubes (Sebert).

Gun-cotton loosely exposed in the open air burns eight times as quickly as
powder (Piobert). A thin disc of gun-cotton may be fired into from a rifle
without explosion; but if the thickness of the disc be increased, an
explosion may occur. The effect of gun-cotton in mines is very nearly the
same as that of dynamite for equal weights. It requires, however, a
stronger detonator, and it gives rise to a larger quantity of carbonic
oxide gas. Gun-cotton should be neutral to litmus, and should stand the
Government heat test--temperature of 150 deg. F. for fifteen minutes (see page
249). In the French Navy gun-cotton is submitted to a heat test of 65 deg. C.
(= 149 deg. F.) for eleven minutes. It should contain as small a percentage of
soluble nitro-cotton and of non-nitrated cotton as possible.

The products of perfectly detonated gun-cotton may be expressed by the
following equation:--

2C_{12}H_{14}O_{4}(NO_{3})_{6} = 18CO + 6CO_{2} + 14H_{2}O + 12N.

It does not therefore contain sufficient oxygen for the complete
combustion of its carbon. It is for this reason that when used for mining
purposes a nitrate is generally added to supply this defect (as, for
instance, in tonite). It tends also to prevent the evolution of the
poisonous gas, carbonic oxide. The success of the various gelatine
explosives is due to this fact, viz., that the nitro-glycerine has an
excess of oxygen, and the nitro-cotton too little, and thus the two
explosives help one another.

In practice the gases resulting from the explosion of gun-cotton are--
Carbonic oxide, 28.55; carbonic acid, 19.11; marsh gas (CH_{4}), 11.17;
nitric oxide, 8.83; nitrogen, 8.56; water vapour, 21.93 per cent. The late
Mr E.O. Brown, of Woolwich Arsenal, discovered that perfectly wet and
uninflammable compressed gun-cotton could be easily detonated by the
detonation of a priming charge of the dry material in contact with it.
This rendered the use of gun-cotton very much safer for use as a military
or mining explosive.

As a mining explosive, however, gun-cotton is now chiefly used under the
form of tonite, which is a mixture of half gun-cotton and half barium
nitrate. This material is sometimes spoken of as "nitrated gun-cotton."
The weight of gun-cotton required to produce an equal effect either in
heavy ordnance or in smal