These conditions are similar to those under which a mining charge, simply ignited by the cap, burns away slowly under a low pressure (i.e., a miss fire). In a recent communication, P.F. Chalon (_Engineering and Mining Journal_, 1892) says, that in practice nitro-glycerine vapour, carbon monoxide, and nitrous oxide, are also produced as the result of detonation, but he attributes their formation to the use of a too feeble detonator. Nitro-glycerine explodes very violently by concussion. It may be burned in an open vessel, but if heated above 250 deg. C. it explodes. Professor C.E. Munroe gives the firing point as 2O3 deg.-2O5 deg. C., and L. de Bruyn[A] states its boiling point as 185 deg.. He used the apparatus devised by Horsley. The heat of formation of nitro-glycerine, as deduced from the heat of combustion by M. Longuinine, is 432 calories for 1 grm.; and the heat of combustion equals 1,576 cals. for 1 grm. In the case of nitro-glycerine the heat of total combustion and the heat of complete decomposition are interchangeable terms, since it contains an excess of oxygen. According to Dr W.H. Perkin, F.R.S.,[B] the magnetic rotation of nitro-gylcerine is 5,407, and that of tri-methylene nitrate, 4.769 (diff. = .638). Dr Perkin says: "Had nitro-glycerine contained its nitrogen in any other combination with oxygen than as -O-NO_{2}, as it might if its constitution had been represented as C_{3}H_{2}(NO_{2})_{3}(OH)_{3}, the rotation when compared with propyl nitrate (4.085) would be abnormal." [Footnote A: _Jour. Soc. Chem. Ind._, June 1896, p. 471.] [Footnote B: _Jour. Chem. Soc._, W.H. Perkin, 1889, p. 726.] The solubility of nitro-glycerine in various solvents has been investigated by A.H. Elliot; his results may be summarised as follows:--