I 'rut'. If. L. ('aileiuliir. On the T< <"l 



The values of </H;W0 are obtained from those of dp/dO by diflerenti- 

 ating equation (32), thus, 



dUldO = S - (n + 1) r (ilpJdO - np/6). 



It will l>e observed that the values of the total heat in the above 

 table agree very closely with those of Regnault between 60 and 90% 

 where his results (according to Griffiths)* are most reliable. The 

 average of his observations over this range is in exact agreement with 

 Table III. At lower temperatures, Regnault's observations are very 

 discordant, but the values given in the table are well supported by 

 those of Griffiths. He finds, for instance, the latent heat to be 572*7 

 calories at 40*2 C., where the table would give 573*1. The unit 

 employed by Griffiths (calorie at 15 C.) is different, so that his value 

 would require to be raised nearly 0*6 cal. to reduce to the same unit, 

 which would make it 573*3 calories at 40*2. There can be no doubt 

 that his observations are entitled to much greater weight than those 

 of Regnault, which are nearly 6 calories larger at this point. The 

 value, 596*7 found by Dieterici with an ice calorimeter,! for the latent 

 heat at C., is 3*2 calories larger than that given in the table. But 

 it must be remembered that observations of the latent heat at C. are 

 not at all easy, and that there is some uncertainty about the unit 

 employed by Dieterici, as he finds by the same method the value of 

 the mean specific heat of water between and 100 C., about 1 per 

 cent, larger than Reynolds and Moorby or Callendar and Barnes. It 

 is possible that his result might agree with Table III if it could be 

 reduced to the same units. 



Entropy of Wvder and Steam. 



The entropy of water, < fr , is readily calculated from a table of the 

 values of the specific heat when the variation of the specific heat is 

 known. Since, however, the specific heat is nearly equal to unity, we 

 may write, 



<t> w = \og*6/8 + d<t> (33), 



where d<j> is the small difference of the value at any temperature from 

 the value log e 0/0, calculated on the assumption of constant specific 

 heat. The values of d<j> given in the following table have been calcu- 

 lated from the table of values of the specific heat given by Callendar 

 and Barnes. J It will be seen that the values of d<f> are very small at 

 temperatures below 100 C., but increase rapidly at higher tempera- 

 tures. Above 200 C. the values of the specific heat of water are so 

 uncertain that it is not possible to calculate the properties of steam 

 satisfactorily by any method. The values of dh/6 = (h- /)/# are also 



* ' Boy. Soc. Proc.,' December, 1894. 

 t 'Wied. Ann., 1 vol. 37, p. 504, 1899. 

 J ' Brit. Assoc. Kep.,' 1899. 



