80 



HEAT. 



Fig. 60, representing all the results, is taken from his paper. 



General Results. Probably in all substances the specific heat 

 changes with the temperature In general it increases as the tempera- 

 ture rises, so long as the substance does not change its state. A specific 

 heat increasing uniformly with rise of temperature, would be repre- 

 sented by 



s=a+fit 



but it is only over small ranges that such a simple formula represents 

 the results of experiments. Over larger ranges they may be better 

 represented by 



and no doubt, if the results were accurate, they would be still better 



<K> 9 . - . 



O 20 40 60 SO' I0<f 



* Temperature 



FIG. 60. Results of Different Experiments on the Specific Heat of Water. 



represented by the addition of terms containing higher powers of t. But 

 at present the errors of experiment are so great that it is useless to 

 trouble about these higher powers. 



We probably have the most accurate knowledge of the variation of 

 specific heat in the case of aniline over the range from 15 to 52. This 

 was determined by Griffiths (Phys. Soc., 13, 1894) by the method of 

 electrical heating. He selected aniline in place of water, on account of 

 its great suitability as a calorimetric liquid, for it is easily obtainable in 

 a fairly pure state, it has a low vapour pressure at ordinary tempera- 

 tures, and with its specific gravity, 1'02, and specific heat, '52, its 

 capacity for heat per unit volume is only half that of water. The 

 specific heat at t* is given by Griffiths in terms of the calory at 15 as 



s = -5156 + (t- 20)-0004 + (t - 20) 2 '000002. 



Regnault has obtained the specific heat of a number of liquids. From 

 these we may select alcohol, for which he gives, in terms of the calory 

 atO, 



8 ="54755 + -002242*+ -000006618* 8 



