322 MR. E. H. GRIFFITHS ON THE LATENT 
Mean thermal unit 9952 __-0:9957 
Thermal unit at 15° OC. 9995 = 1 

: ‘011 
in place of a . 
It is apparent that there is sufficient evidence to justify scepticism as to the 
validity of the commonly accepted ratio, and J] hope that the demonstration of this 
uncertainty may quicken further investigation into the actual value of this important 
constant. 
Note (by Dr. J. Jory, F.R.S.) on the Ratio of the Latent Heat of Steam to the 
Specific Heat of Water. 
Upon receiving from Mr. GRIFFITHS a copy of the abstract of his paper on the 
latent heat of steam, I determined upon making some experiments with the steam 
calorimeter on the ratio of the latent heat of steam to the mean specific heat of 
water over the range air temperature 12° to 100°. Pending the completion of a form 
of the calorimeter which will enable me to make this comparison over suitable and 
definite ranges of temperature, I gladly add, at Mr. Grirrirus’ request, the following 
note on the experiments already made. 
The weight of water operated upon was 12°8545 grms. This was enclosed in a 
thin blown glass bulb, sealed while the water was boiling, and having an internal 
volume of 15°714 cub. centims. Ten experiments were made—these were in close 
agreement. The mean initial temperature was 11°89; the mean steam temperature 
99°96. The first temperature was determined by 2 Kew-corrected thermometer 
reading tenths on an open scale; the second temperature determined by a standard 
barometer. ‘The mean weight of steam condensed was 2°32917 grms. 
To correct this for the effect of the glass vessel, six experiments were made on the 
latter when containing dry air only. Further corrections were made (a) for eyapo- 
ration within the vessel when containing water; (b) for buoyancy or displacement 
effect on the apparent weight of the vessel, the densities being not quite the same in 
the experiments on the filled and empty vessel; (c) for the specific heat of the air 
contained in the vessel when empty of water. A total subtractive correction of 
0°2298 grm. was obtained. 
If we now calculate the mean specific heat of water between 11°89 and 99°-96, 
assuming the value of the latent heat of steam given by Mr. Grirritus’ formula, 2.e., 
L = 596°73 — ‘6010 6, where @ has the value 99°'96, we get 
20994 x 536°66 
Om bea ay 
T have little doubt that this will remain —closely—the mean specific heat, 12°-100°, 
according to the steam calorimeter. It will, of course, be necessary to check the 
result by further experiments. It is true I formerly made experiments in the steam 
