gas produced, heat developed, etc.; and this method is excellent for obtaining a fair idea of the specific pressure of any new explosive that may be brought forward, and determining whether it is worth while to investigate it further; but the explosives differ so much from each other in point of sensitiveness, weight, physical condition, velocity of explosive wave, influence of temperature and humidity, that we cannot determine from mere theoretical considerations all that we would like to know.  Various methods of arriving at comparative values have been tried, but the figures are very variable, as will be seen by the following tables.  Berthelot’s commission, some ten years ago, exploded ten to thirty grammes of each in 300 pound blocks of lead and measured the increased size of the hole thus made.  The relative result was: 

No. 1 dynamite       1.0
Dry gun-cotton       1.17
Nitro-glycerine      1.20

Powder blew out and could not be measured.

Mr. R.C.  Williams, at the Boston Institute of Technology, in the winter of 1888 and 1889, tried the same method, but used six grammes in forty-five pound blocks of lead.  He obtained a relative result of—­

  No. 1 dynamite 1.0
  Dry gun-cotton 1.37
  Nitro-glycerine 2.51
  Explosive gelatine 2.57
  Forcite gelatine 2.7
  Warm nitro-glycerine 2.7
  Gunpowder 0.1

The powder gave great trouble in this case, also, by blowing out.

M. Chalon, a French engineer, obtained some years ago, with a small mortar, firing a projectile of thirty kilos and using a charge of ten grammes of each explosives, the following ranges: 

                              Meters. 
  Blasting powder 2.6
  No. 1 dynamite 31.4
  Forcite of 75 per cent.  N.G. 43.6
  Blasting gelatine 45.0

Roux and Sarran obtained by experiments in bursting small bomb shells the following comparative strengths of ranges: 

Powder                           1.0
Gun-cotton                       6.5
Nitro-glycerine                 10.0

In actual blasting work the results vary altogether with the nature of the material encountered, and with the result that is desired to be accomplished, viz., throwing out, shattering, or mere displacement.

Chalon gives for quarrying: 

Powder                                                      1
Dynamite No. 2, containing 50 per cent. nitro-glycerine     3

For open blasting: 

  Dynamite No. 3, containing 30 per cent.  N.G. 1.0
  Dynamite No. 1, containing 75 per cent.  N.G. 2.5
  Blasting gelatine 3.5

For tunneling: 

  Dynamite No. 3, containing 30 per cent.  N.G. 1
  Dynamite No. 1, containing 75 per cent.  N.G. 3
  Explosive gelatine 19