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
formulæ[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