226 Mr. W. Makower on a Determination of the 



the chemical induction and chemical deduction periods (see 

 p. 391): — 



Since Telocity of reaction follows the law of action of mass, 

 when the molecules taking part in the reaction have attained, 

 under the influence of light, a constant value of their chemical 

 potentials, the same law of mass-action must also be the 

 governing principle for the velocity of reaction at any given 

 moment of the chemical induction and deduction periods, 

 only the velocity constant in the equation for velocity of 

 reaction will vary as the chemical potentials of the reacting 

 substances change. 



Davy Faraday Laboratory of the 

 Boval Institution. November 1902. 



XX. On a Determination of the Ratio of the Specific Heats 

 at Constant Pressure and at Constant Volume for Air and 

 Steam. By Walter Makower, B.Sc, University College, 

 London*. 



Plate I.] 



1. Introduction and General Method. 



THE method employed was similar to tbat used by 

 Lummer and Pringsheim (Smithsonian Contributions 

 to Knowledge, 1898), which consists in allowing the gas 

 under investigation to expand adiabatically and measuring 

 the lowering of temperature caused by such expansion. 



In these experiments the initial and final pressures of the 

 gas were measured on a sulphuric acid gauge, and the change 

 of temperature deduced from the variation of the electrical 

 resistance of a fine platinum-bolometer strip immersed in the 

 gas under investigation. The gases experimented upon were 

 air, oxygen, carbon dioxide, and hydrogen, for which the 

 values of the ratio of the two specific heats were found to be 

 1-4:025, 1-3977, 1-2995, 1*4084 respectively. 



The chief modifications introduced in the present investi- 

 gation consist in the substitution of a platinum-thermometer 

 with compensating leads, for the bolometer-strip of Lummer 

 and Pringsheim, who employed a somewhat different device 

 for eliminating errors due to conduction of heat along the 

 leads. Also, at the suggestion of Prof. Callendar, the elec- 

 trical contacts were made by means of a specially constructed 

 automatic mercury switch, instead of by hand. It was also 

 hoped that it might be possible to use smaller quantities of 

 gas than Lummer and Pringsheim had used, and it was 



* Communicated by the Physical Society : read November 14, 1902. 



