$2 CALORIFIC POWER OF FUELS. 



which and in contact with it is the iron spiral. At the 

 instant of lighting a slight noise is made, and soon the ther- 

 mometer begins to rise, showing that the combustion is pro- 

 ceeding. 



Compressed oxygen may be introduced either by a pump 

 drawing the gas from a holder or by using a compressed-gas 

 cylinder. In both cases the gas is used without drying, if 

 the combustible contains hydrogen in quantity enough to 

 saturate the gases formed with water produced by its combus- 

 tion. But if, on the contrary, the combustible has little or 

 no hydrogen, like wood-charcoal for instance, it is not im- 

 material whether the oxygen be dry or not. In this case it 

 is well to use the oxygen moist, or to put a little water in the 

 bomb on the internal walls. By this means a correction for 

 heat of vaporization of water formed by the combustion is 

 obviated. 



Oxygen compressed to 120 atmospheres is nearly dry. 

 Berthelot observes: "The oxygen is, in short, actually or 

 nearly dry, and if it contains aqueous vapor the tension is 

 reduced to one fourth or one fifth on account of the change 

 in volume of the gas during its passage through the bomb. It 

 may be nearly nullified by the cold produced at the instant of 

 filling the bomb. This admitted, we shall have to account in 

 most combustions for the evaporation of the water produced 

 in the bomb; and this is from 2 to 3.5 calories in a bomb of 

 ^ litre (about O.6 pint), or 5 to 6 calories in a bomb of 600 to 

 700 cubic centimetres (37 to 43 cubic inches). These are 

 rather small quantities, it is true; but while they can be 

 neglected in industrial tests, they cannot in rigorously 

 scientific investigations. This correction may, however, be 

 neutralized by putting into the bomb 4 or 5 cc. of water, 

 which should be considered in the calculations. 



When oxygen not previously compressed is used and 

 forced in by a pump, Berthelot recommends passing the gas 

 through a large red-hot copper tube filled with oxide of the 



