HEAT OF EVAPORATION OF WATER. 273 
If the calorimeter at the commencement and end of an experiment was at exactly 
the same temperature as the surrounding walls, then if their temperature was 
unchanged, the term q would vanish; but although this term throughout these 
experiments was of small dimensions, it could not be entirely ignored. 
Let @ and 6”, be the temperature of the surrounding walls at the beginning 
and end of an experiment; suppose the calorimeter temperature (6,) to exceed the 
surrounding temperature by d’ at the commencement and d” at the end of an 
experiment. Then fall in temperature of calorimeter 
=(0),+ a’) —(0 +a’). 
Hence the heat given out by the calorimeter in consequence of this fall in tempera- 
ture is 
Co, (0 + @’) — (0% + dD}, 
where C,, is the capacity for heat of calorimeter and contents at the temperature 0). 
If we neglect any small loss by radiation, &c., due to the differences @’ and d” 
between the temperature of the calorimeter and the surrounding walls, we may 
conclude that the whole of the heat thus evolved by the calorimeter was expended iu 
the evaporation of water, hence 
pes Ch (UO) Pode ee. ee) 
Hence 
ML = ae + Q, X t + Oy, (0% — 0%) + (@ — a"). (A) 
Tn order to convey an idea of the relative importance of the terms in equation (4) 
I will here give the approximate mean value of each term resulting from the experi- 
ments described in succeeding pages. 


TABLE II. 
Qete. Qs bse =q. 
When 
G =Venigsd 2. 2 5 6 « 2150 19:2 +16 
G = Beachy . og 5c 2305 32°9 +12 
Ge ander — ome ene 1752 32°9 ae 19) 





* This apparently clumsy method of representing the quantity of heat evolved or taken up by the 
calorimeter was adopted because, as the method of experiment involved separate determinations of 
6", 0", d' and d’, the actual temperature of the calorimeter at any time could only be obtained in this 
manner. 
MDCCCXCYV,—A. 2N 
