330 REPORTS ON THE STATE OF SCIENCE, 



The energy of gas-engine mixture at 1400° according to Clerk, 

 Holborn and Henning, and Langen respectively would be as follows ;— 



Clerk 8300 



Holborn and Henning , 7700 



Langen ........ 8300 



It will be seen that the agreement between Clerk and Langen is close, 

 both being about 8 per cent, higher than Holborn and Henning. But 

 it is to be observed that this temperature is just outside the range of all 

 three sets of experiments. 



The Committee are of opinion that values of the energy obtained from 

 explosion records are not subject to any very great errors on account of 

 heat-loss by conduction to the walls of the vessel, nor on account of incom- 

 plete combustion, but that they are affected by errors of quite unknown 

 amount due, first, to heat radiated, and secondly to the want of thermal 

 equilibrium at the time when the pressure is measured. For the purpose 

 of testing the first of these conclusions, it is very desirable that further 

 experiments should be made on explosions in vessels of greatly different 

 size but of similar form. The opinion entertained by the Committee that 

 incomplete combustion is a surface-phenomenon, on which this conclusion 

 as to the validity of the method is based, also requires further confirma- 

 tion. As regards the second conclusion further experiment on the actual 

 amount of heat radiated by burning gas is urgently required, and also 

 experiments to confirm or negative the effect of the nature of the wall 

 surface upon the pressure reached in an explosion. The effect of want 

 of thermal equilibrium can be determined up to a point by calculation ; 

 but before such calculation can be usefully made, it is desirable that 

 further information should be obtained as to the temperature distribution 

 after an explosion, especially in the neighbourhood of the walls. It 

 should not be difficult to get an idea of this sufficiently accurate for the 

 purpose by means of platinum thermometers. 



The most hopeful way, however, of making use of explosions to give 

 definite information as to the properties of gases would appear to ba to 

 directly measure the heat lost in the explosion, as if this be done it is 

 possible to defer the pressure measurement until such time as equilibrium 

 conditions, except those that depend on the surface of the vessel, have 

 been attained. 



The Measurement of Temperature. 



In all the experiments for the determination of the energy function 

 which have been described above the measurement of the temperature is 

 ultimately based upon the pressure or volume changes of the gas. In the 

 constant-pressure experiments of Holborn and Henning the temperature 

 of the gas before entering the calorimeter was measured by means of a 

 thermo-couple which had been compared with a constant-volume nitrogen 

 thermometer up to 1600° C. In the explosion experiments the mean 

 tempernture of a gas is inferred from its pressure. Similarly, in the 

 analysis of the gas-engine diagrams, the gas ia itse'f the thermometer. 

 The mean temperature at any point is taken as proportional to the product 

 pv, and the actual temperature at one point in the cycle (a knowledge 



