of toluene,[A] are stated to lower the freezing point of nitro-glycerine to -20 deg.C. without altering its sensitiveness and stability.  The subject has been investigated by S. Nauckhoff,[B] who states that nitroglycerine can be cooled to temperatures (-40 deg. to -50 deg.  C.) much below its true freezing point, without solidifying, by the addition of various substances.  When cooled by means of a mixture of solid carbon, dioxide, and ether, it sets to a glassy mass, without any perceptible crystallisation.  The mass when warmed to 0 deg.C. first rapidly liquefies and then begins to crystallise.  The true freezing point of pure nitro-glycerine was found to be 12.3 deg.C.  The technical product, owing to the presence of di-nitro-glycerine, freezes at 10.5 deg.  C. According to Raoult’s law, the lowering of the freezing point caused by m grms. of a substance with the molecular weight M, when dissolved in 100 grms. of the solvent, is expressed by the formula:  [Delta] = E(m/M), where E is a constant characteristic for the solvent in question.  The value of E for nitro-glycerine was found to be 70.5 when calculated, according to Van’t Hoff’s formula, from the melting point and the latent heat of fusion of the substance.  Determinations of the lowering of the freezing point of nitro-glycerine by additions of benzene, nitro-benzene, di-nitro-benzene, tri-nitro-benzene, p.-nitro-toluene, o.-nitro-toluene, di-nitro-toluene, naphthalene, nitro-naphthalene, di-nitro-naphthalene, ethyl acetate, ethyl nitrate, and methyl alcohol, gave results agreeing fairly well with Raoult’s formula, except in the case of methyl alcohol, for which the calculated lowering of the freezing point was greater than that observed, probably owing to the formation of complex molecules in the solution.  The results show that, in general, the capacity of a substance to lower the freezing point of nitro-glycerine depends, not upon its freezing point, or 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.