HEAT OF EVAPORATION OF WATER. 2638 
During the summer of 1893 I was assisted by Mr. G. M. Crarx, B.A., and 
throughout 1894 by Mr. C. GREEN, Scholar of Sidney Sussex College, and I am glad 
to have this opportunity of acknowledging my indebtedness to both those gentlemen. 
As frequent references have to be given to two former papers, I denote them as 
follows :-— 
Paper J.” “ The Mechanical Equivalent of Heat,” ‘Phil. Trans.,’ vol. 184 
(1893), A, pp. 361-504. 
Paper A.” ‘The Influence of Temperature upon the Specific Heat of Aniline,” 
‘Phil. Mag.,’ January, 1895. 
Section I].—HuistTorIcAt. 
The following is, I think, a fairly complete table of results published since the 
year 1843 :— 







TABLE I. 
| | No. of | 
| o. of | 
|Temperature.| Observer. experi- | a aie Reference. 
ments. | ; ’ 
| 
| 0° Dimrerrcr. .| 20 | 595°52-598:84 | 5968 | ‘Wied. Ann,’ vol. 37, 1889 
=F tm 42 1GH| Iie 6 ol PR | eS oe ‘Mémoir. de l’Acad.,’ vol. 21, 1847 
63°-88° a baie | aes 5b Ae eal| Bs fe 45 
| 99°88 » + -| 44. | 583:3-588:4 | 536-67 i dh fs 
99°-81 FAVRE and 3 | 632°59-541°77 | 53577 | ‘Ann. de Chimie,’ vol. 37, 1853 
SILBERMANN | 
100° | ANDREWS . . 8 | 5308-543-4 535°9 | ‘Chem. Soc. Journ.,’ 1849 
| 100° BERTHELOT . 3 535°2-537°2 5362 | ‘Comptes Rendus,’ vol. 85, 1877 
100° SCHALL. . . No de tails given 5320 | ‘ Ber. d. Chem. Ges.,’ vol. 17, 1884 
Pe lLOOSLG: Harrog and 5 523°61-525'87 | 524-60 | ‘Manchester Phil. Soc. Proc.,’ 
HArKER* | 1893-4. 
119°-194° | Reenavtt. .| 73 | a Me ‘Mémoir. de l’Acad.,’ vol. 21, 1847 
| 
| \ 


The values obtained by WINKELMANN (‘ Wied. Ann.,’ vol. 9, 1880) are not included 
in the above table, as they are not based on independent experiments, but deduced 
from the observations of REGNAULT. 
I do not propose to examine at length any of the above determinations except those 
* Tt is right to add that Messrs. Hartoc and Harxer state that these are the results of ‘‘ Preliminary 
Experiments,” and should not be regarded as giving their final conclusions. I do not, therefore, include 
their work in my criticisms. 
+ It must be remembered that all the above values of L (with the exception of Disrmrici’s) depend 
upon some assumption as to the changes in the specific heat of water caused by changes in temperature, 
for they are either deduced from “ the total heat of steam,” or depend upon the observation of the rise 
or fall in temperature of a certain mass of water. Again, as the nature of the thermal unit adopted by 
the observer is, in some cases, doubtful, an uncertainty of an order of about 1 per cent. is thus 
introduced. 
