ON EVAPORATION AND DISSOCIATION. 
89 
boiled at 34‘9° at 752 mms. pressure. Favre and Silbermann found 91'11 calories 
(‘ Annales de Chimie,’ vol. 37, 1853, p. 465). Regnault (‘ Memoires de l’Acaddmie,’ 
vol. 26, p. 881) gives a formula for calculating the total heat of vaporisation from 0°; 
it is 
X = a-\- bt-\- ct^, 
where a = 94, b = 0-45, and c = — (P00055556. 
From this formula the heat of vaporisation at 0° = 94 calories, but for higher 
temperatures the specific heat of ether is required, for calculating which he gives the 
formula 
Q — cit -}- bl^, 
where Q is the total quantity of heat required to raise 1 grm. of ether from 0° to t ; 
log a = 1‘7234538 ; and log b = 4’4711026. Four experiments were made, of which 
the results of only three were employed in calculating the constants, although the 
fourth experiment was moderately concordant with the others; the range was only 
from —30° to +32°. Taking into consideration the small number of experiments, 
and the not very close agreement between the result of the second experiment and 
the value calculated from the formula (calculated, Q= 15‘821 ; observed, Q = 15‘930), 
it is doubtful whether these constants would hold good for temperatures much higher 
than 35°. Regnault made two series of experiments, of which there were seven 
observations in the first and four in the second, on the heats of vaporisation of ether. 
The ether employed in the first series was purified by the ordinary methods, and 
distilled from time to time with lime to lemove acids and water. In the second 
series, including experiments at very low pressures, the ether was purified “ with the 
greatest care,” and kept in a stoppered flask. Nevertheless, on distillation, a quantity 
of less volatile liquid remained behind, having, as he states, the percentage composition 
of ether. This modification, according to him, is absent from ether recently distilled, 
but forms after some months (see remarks on p. 82). In the second series the weight 
of the residual liquid in the calorimeter was always subtracted from the total weight, 
the liquid having been distilled from the calorimeter. The following Table gives the 
individual results of Regnault’s experiments, and also the total heats at the same 
temperatures, calculated by means of his formula. The first four experiments were 
made with the carefully purified ether. 
Temperature. 
Total heat. 
Temperature. 
Total heat. 
Observed. 
Calculated. 
Observed. 
Calculated. 
O 
- 3-7 
92-235 
92-343 
34°83 
109-117 
109-0 
+ 7-51 
95-370 
97-35 
90-05 
128-900 
, , 
12-9 
97-282 
99-72 
93-85 
130-880 
, , 
15-5 
98-801 
100-84 
108-80 
138T96 
136-38 
1715 
101-278 
101-56 
120-90 
140781 
, , 
21-95 
104-366 
• • 
MDCCCLXXXVII.-A. N 
