348 
DR. A. DUPRE ON THE SPECIFIC HEAT AND OTHER 
10 per cent, mixture. 
In the formation of 5 grins, of a 10 per cent, mixture are evolved, at a temperature of 
5*8 C., 23-65 units of heat. 
19-64 C., 20-93 
Difference 2-72 ,, ,, 
30 per cent, mixture. 
In the formation of 5 grins, of this mixture are evolved, at a temperature of 
6-4 C., 45*75 units. 
17-38 C., 44-74 „ 
Difference 1"01 ,, 
Endeavours to estimate the heat evolved at higher temperatures led to still less satis- 
factory results. At the end of every experiment the mixture was found to be weaker 
in spirit than it should have been, from the amounts of water and alcohol taken ; and 
this loss of alcohol of course diminished the amount of heat evolved. This loss took 
place although the mixing was effected in a closed vessel. Nevertheless these experiments 
show distinctly that less heat is evolved at the higher temperature. 
Calculating, as in the previous mixture, the temperature at which no heat would be 
evolved on mixing, the following temperatures are obtained: — 152°, 175°, 173°, 154°, 
162°, 160°, 147°, 175°, and 146° for strengths of 10, 20, 30, 40, 50, 60, 70, 80, and 90 
per cent, respectively; the mean of these temperatures is 156° C. These temperatures 
differ apparently somewhat widely, and yet the maximum deviation from the mean found 
corresponds to a small error only in the estimation of the specific heat of the corresponding 
mixture. Thus the maximum differences are found at an alcoholic strength of 20 and 
80 per cent. The specific heat of these two mixtures as found is 95-91 and 69-99, 
whereas the specific heat corresponding to the above mean temperature of 156° would be 
96-42 and 69*54 ; the difference in either case is less than t 4q of the total value. A 
glance at Table II. will show that in this, as in the previous mixture, the rate of expansion 
seems incompatible with the supposition that the high specific heat observed is caused 
by dissociation. For weak and for strong mixtures the rate of expansion is below the 
mean, for mixtures of middle strength above the mean ; in the first two cases the 
amount of contraction is greater, in the last case it is less, the higher the temperature. 
The specific heat does not, however, show any corresponding change. 
