|OH
C_{3}H_{5}|OH,
|OH

which is a tri-hydric alcohol, and which occurs very widely distributed as
the alcoholic or basic constituent of fats, the hydrogen atoms are
replaced by the NO_{2} group, to form the highly explosive compound,
nitro-glycerine. If one atom only is thus displaced, the mono-nitrate is
formed thus,

|ONO_{2}
C_{3}H_{5}|OH;
|OH

and if the three atoms are displaced, C_{3}H_{5}(ONO_{2})_{3}, or the tri-
nitrate, is formed, which is commercial nitro-glycerine.

Another class, the nitro-celluloses, are formed from cellulose,
C_{6}H_{10}O_{5}, which forms the groundwork of all vegetable tissues.
Cellulose has some of the properties of the alcohols, and forms ethereal
salts when treated with nitric and sulphuric acids. The hexa-nitrate, or
gun-cotton, has the formula, C_{12}H_{14}O_{4}(ONO_{2})_{6}; and
collodion-cotton, pyroxylin, &c., form the lower nitrates, i.e., the
tetra- and penta-nitrates. These last are soluble in various solvents,
such as ether-alcohol and nitro-glycerine, in which the hexa-nitrate is
insoluble. They all dissolve, however, in acetone and acetic ether.

The solution of the soluble varieties in ether-alcohol is known as
collodion, which finds many applications in the arts. The hydrocarbon