__________________________________________________________________________ | | Maximum | | Distance | | at which | | Detonation | | occurred. | | CM. | | | Gun-cotton | 10 | Nitro-glycerine 86.5 nitro-cotton | | 9.5, camphor 4 per cent. Explosive gelatine | 20 | NH_{4}NO_{3} 5 parts, (camphorated) | | C_{6}H_{4}(N0_{3})_{2} 1 part. Judson powder, R.R.P. | 25 | Emmensite (No. 259) | 30 | Rack-a-rock | 32 | KClO_{3} 79 parts, | | C_{6}H_{5}(NO)_{2} 21 parts. Bellite | 50 | Forcite No. 1 | 61 | Kieselguhr dynamite No. 1 | 64 | 75 per cent. nitro-gycerine. Atlas powder No. 1 | 74 | __________________________|____________|_________________________ CHAPTER IX. _DETERMINATION OF THE RELATIVE STRENGTH OF EXPLOSIVES._ Effectiveness of an Explosive--High and Low Explosives--Theoretical Efficiency--MM. Roux and Sarrau's Results--Abel and Noble's--Nobel's Ballistic Test--The Mortar, Pressure, or Crusher Gauge--Lead Cylinders-- The Foot-Pounds Machine--Noble's Pressure Gauge--Lieutenant Walke's Results--Calculation of Pressure Developed by Dynamite and Gun-Cotton-- Macnab's and Ristori's Results of Heat Developed by the Explosion of Various Explosives--Composition of some of the Explosives in Common Use for Blasting, &c. ~The Determination of the Relative Strength of Explosives.~--Explosives may be roughly divided into two divisions, viz., those which when exploded produce a shattering force, and those which produce a propulsive force. Explosives of the first class are generally known as the high explosives, and consist for the most part of nitro compounds, or mixtures of nitro compounds with other substances. Any explosive whose detonation is very rapid is a high explosive, but the term has chiefly been applied to the nitro-explosives. The effectiveness of an explosive depends upon the volume and temperature of the gases formed, and upon the rapidity of the explosion. In the high explosives the chemical transformation is very rapid, hence they exert a crushing of shattering effect. Gunpowder, on the other hand, is a low explosive, and produces a propelling or heaving effect. The maximum work that an explosive is capable of producing is proportionate to the amount of heat disengaged during its chemical transformation. This may be expressed in kilogrammetres by the formula 425Q, where Q is the number of units of heat evolved. The theoretical efficiency of an explosive cannot, however, be expected in practice for many reasons.