eries. They are called ortho, meta,
or para compounds, depending upon the position of NO_{2} groups
introduced.

Certain regularities have been observed in the formation of nitro-
compounds. If, for example, a substance contains alkyl or hydroxyl groups,
large quantities of the para compound are obtained, and very little of the
ortho. The substitution takes place, however, almost entirely in the meta
position, if a nitro, carboxyl, or aldehyde group be present. Ordinary
phenol, C_{6}H_{5}.OH, gives para- and ortho-nitro-phenol; toluene gives
para- and ortho-nitro-toluene; but nitro-benzene forms meta-di-nitro-
benzene and benzoic acid, meta-nitro-benzoic acid.[A]

[Footnote A: "Organic Chemistry," Prof. Hjelt. Translated by J.B. Tingle,
Ph.D.]

If the graphic formula of benzene be represented thus (No. 1), then the
positions 1 and 2 represent the ortho, 1 and 3 the meta, and 1 and 4 the
para compounds. When the body phenol, C_{6}H_{5}.OH, is nitrated, a
compound is formed known as tri-nitro-phenol, or picric acid,
C_{6}H_{2}(NO_{2})_{3}OH, which is used very extensively as an explosive,
both as picric acid and in the form of picrates. Another nitro body that
is used as an explosive is nitro-naphthalene, C_{10}H_{6}(NO_{2})_{2}, in
roburite, securite, and other explosives of this class. The hexa-nitro-
mannite, C_{6}H_{8}(ONO_{2})_{6}, is formed

[Illustration: No. 1]

[Illustration: META-DINITRO-BENZENE No.2]

by treating a substance known as mannite, C_{6}H_{8}(OH)_{6}, an alcohol
formed by the lactic acid fermentation of sugar and closely related to the
sugars, with nitric and sulphuric acids. It is a solid substance, and very
explosive; it contains 18.58 per cent. of nitrogen.

Nitro-starch has also been used for the manufacture of an explosive.
Muhlhauer has described (_Ding. Poly. Jour._, 73, 137-143) three nitric
ethers of starch, the tetra-nitro-starch, C_{12}H_{16}O_{6}(ONO_{2})_{4},
the penta- and hexa-nitro-starch. They are formed by acting upon potato
starch dried at 100 deg. C. with a mixture of nitric and sulphuric acids at a
temperature of 20 deg. to 25 deg. C. Rice starch has also been used in its
production. Muhlhauer proposes to use this body as a smokeless powder, and
to nitrate it with the spent mixed acids from the manufacture of nitro-
glycerine. This substance contains from 10.96 to 11.09 per cent. of
nitrogen. It is a white substance, very stable and soluble even in cold
nitro-glycerine.