often give
as high a percentage as 12.6.

We shall only describe the manufacture of the two forms known as soluble
and insoluble, and shall refer to them under their better known names of
gun-cotton and collodion-cotton. The following would, however, be the
formulae[A] and percentage of nitrogen of the complete series:--

Hexa-nitro-cellulose C_{12}H_{14}O_{4}(NO_{3})_{6} 14.14 per cent.
nitrogen.
Penta-nitro-cellulose C_{12}H_{15}O_{5}(NO_{3})_{5} 12.75 per cent.
nitrogen.
Tetra-nitro-cellulose C_{12}H_{16}O_{6}(NO_{3})_{4} 11.11 per cent.
nitrogen.
Tri-nitro-cellulose C_{12}H_{17}O_{7}(NO_{3})_{3} 9.13 per cent.
nitrogen.
Di-nitro-cellulose C_{12}H_{18}O_{8}(NO_{3})_{2} 7.65 per cent.
nitrogen.
Mono-nitrocellulose C_{12}H_{19}O_{9}(NO_{3}) 3.80 per cent.
nitrogen.

[Footnote A: Berthelot takes C_{24}H_{40}O_{20} as the formula of
cellulose; and M. Vieille regards the highest nitrate as
(C_{24}H_{18}(NO_{3}H)_{11}O_{9}). _Compt. Rend._, 1882, p. 132.]

~Properties of Gun-Cotton.~--The absolute density of gun-cotton is 1.5.
When in lumps its apparent density is 0.1; if twisted into thread, 0.25;
when subjected, in the form of pulp, to hydraulic pressure, 1.0 to 1.4.
Gun-cotton preserves the appearance of the cotton from which it is made.
It is, however, harsher to the touch; it is only slightly hygroscopic (dry
gun-cotton absorbs 2 per cent. of moisture from the air). It possesses the
property of becoming electrified by friction. It is soluble in acetic
ether, amyl acetate, and acetone, insoluble in water, alcohol, ether,
ether-alcohol, methyl-alcohol, &c. It is very explosive, and is ignited by
contact with an ignited body, or by shock, or when it is raised to a
temperature of 172 deg. C. It burns with a yellowish flame, almost without
smoke, and leaves little or no residue. The volume of the gases formed is
large, and consists of carbonic acid, carbonic oxide, nitrogen, and water
gas. Compressed gun-cotton when ignited often explodes when previously
heated to 100 deg. C.

Gun-cotton kept at 80 deg. to 100 deg. C. decomposes slowly, and sunlight causes
it to undergo a slow decomposition. It can, however, be preserved for
years without undergoing any alteration. It is very susceptible to
explosions by influence. For instance, a torpedo, even placed at a long
distance, may explode a line of torpedoes charged with gun-cotton. The
velocity of the propagation of the explosion in metallic