208 M. Achille Cazin on Internal Work in Gases. 



curve X X above the axis of the abscissa? present. They may be 

 due to several causes — such as the difference of temperature ac- 

 quired during the expansion by the various parts of the gaseous 

 mass, the difference of the specific heats, that of the conducti- 

 bility, and, finally, that of the emissive and absorbent powers. 



Let us first compare hydrogen and air. Both must un- 

 dergo almost the same thermometric effects; for we have ap- 

 proximately, for the gas expanded in A and the gas compressed 

 in B, the usual formula 



l + «* __(p>nr 



l+cd i ~\p'J ' 

 with 



K=l-41. 



Besides, these two gases have the same specific heat for a con- 

 stant volume, and also the same emissive or absorbing-power ; 

 but they have not the same conductivity. That of hydrogen 

 is the greatest. Hence the less the conductivity the higher the 

 curve X X rises. What can be the effect of conductivity ? The 

 variations of temperature due to the action of the sides will be 

 more rapid for hydrogen than for air. If the temperature of the 

 total mass is greater than the temperature of the sides when the 

 mixture is effected, it will descend more rapidly; hence the 

 maximum of h must be less for hydrogen, and the curve must 

 reach the axis of the abscissa? more quickly. 



Let us now compare air and carbonic acid. The thermome- 

 tric effects are less for the latter, and the specific heat is greater ; 

 it is the same with regard to its emissive or absorbing-power. 

 As to the conductivity, it cannot differ much. The first cause 

 acts in a direction contrary to the other two : it tends to dimi- 

 nish the quantities of heat taken up or given off by the sides, 

 and consequently to lower the maximum of the curve XX; the 

 other two causes tend to raise it. There may be compensation; 

 and we cannot foresee the direction of the resulting effect. But 

 experiment has given the same maximum, so that we can admit 

 the compensation. 



These various considerations appear sufficient to enable me to 

 give a complete explanation of all the particular points which 

 my experiments present. 



We can "calculate approximately the temperatures which cor- 

 respond to the various stages of an experiment. 



The mixture is completely effected at the moment the curve 

 X X reaches its maximum ; the greatest value observed is 36 mil- 

 lims. of sulphuric acid, which represents 4 millims. of mercury. 

 The excess of temperature of the gaseous mass being 8t, we have, 

 for t = 10°,;? = 760, Sp = 4, 



