its chemical composition or constitution, but upon its molecular weight.
Nauckhoff states that a suitable substance for dissolving in nitro-
glycerine, in order to lower the freezing point of the latter, must have a
relatively low molecular weight, must not appreciably diminish the
explosive power and stability of the explosive, and must not be easily
volatile at relatively high atmospheric temperatures; it should, if
possible, be a solvent of nitro-cellulose, and in every case must not have
a prejudicial influence on the gelatinisation of the nitro-cellulose.

[Footnote A: Eng. Pat. 25,797, November 1904.]

[Footnote B: _Z. Angew. Chem._, 1905, 18, 11-22, 53-60.]

~Manufacture of Nitro-Glycerine.~--Nitro-glycerine is prepared upon the
manufacturing scale by gradually adding glycerine to a mixture of nitric
and sulphuric acids of great strength. The mixed acids are contained in a
lead vessel, which is kept cool by a stream of water continually passing
through worms in the interior of the nitrating vessel, and the glycerine
is gradually added in the form of a fine stream from above. The
manufacture can be divided into three distinct operations, viz.,
nitration, separation, and washing, and it will be well to describe these
operations in the above order.

~Nitration.~--The most essential condition of nitrating is the correct
composition and strength of the mixed acids. The best proportions have
been found to be three parts by weight of nitric acid of a specific
gravity 1.525 to 1.530, and containing as small a portion of the oxides of
nitrogen as possible, to five parts by weight of sulphuric acid of a
specific gravity of 1.840 at 15° C., and about 97 per cent. of mono-
hydrate. It is of the very greatest importance that the nitric acid should