HEAT OF WATER, WITH EXPERIMENTS BY A NEW METHOD. 
1 1 
per mean calorie from the mean of the values given by Bunsen 15’41, Schuller 
and Wartha I5'44, and Velten 15*47. Taking Rowland’s values for tlie 
mechanical equivalent from 0° C. to 30° C., and assuming a linear increase from 
30° C. to 100° C. to fit with his own value for the mean calorie, Dieterici deduced a 
table {loc. cit., p. 441) for the variation of the specific heat from 0° C. to 100° C., 
which has been frequently quoted and employed for reducing observations. According 
to this table, the mean calorie exceeded that at 20° C. by 1’5 per cent. The specific 
heat at 90° C. was 3 per cent, greater than the value subsequently found by the 
continuous-electric method, but appeared to be in fair agreement with older 
observations. 
Dieterici’s later determinations of the mean calorie (‘Ann. Phys.,’ 16, p. 593, 1905) 
by a similar method, in which the current was reduced to 0’05 ampere and the 
resistance increased to 40 ohms in order to diminish errors due to conduction and 
generation of heat in the leading wires, gave a result 4'1925 joules per gr. ° C., 
exceeding the value 4’187 given by the continuous-electric method by only 1‘4 in 
1,000, which is almost, if not quite, within the possible limits of error of the ice- 
calorimeter. Accepting Dieterici’s value of the specific heat at 20° C., namely, 
0'9974 in terms of the mean calorie, his value for the mechanical equivalent at 20° C. 
would be 4T815, which agrees to 1 in 3,000 with the continuous-electric method. 
Dieterici’s value of the calorie at 20° C. has accordingly been taken in place of the 
mean calorie in reducing his results for comparison with those of other observers. It 
should be remarked, however, that the rate of heat supply in his experiments with 
the ice-calorimeter was 300 times smaller than in the continuous-electric method, and 
that, in order to obtain equally good results with the ice-calorimeter, it would be 
necessary that the uncertainty of the heat-loss should also be 300 times smaller, the 
probability of which is open to doubt. 
Dieterici also redetermined the constant of the ice-calorimeter by an improved 
method, employing sealed tubes of quartz-glass to contain the water at 100° C. The 
value thus found was 15"491 mgr. per mean calorie, exceeding the value previously 
employed by 1 in 300. His results by the same method for the mean specific heat 
from 0° C. to t° C., reduced to his calorie at 20° C. as unit, are indicated by the 
diagonal crosses in figs. 1 and 2. Between 0° C. and 100° C., his results, as shown hi 
fig. 2, agree to 1 in 1,000 with my formula, except for one observation at 14°'6 C., 
where, as he admits, an inferior degree of accuracy was to be expected. For 
temperatures above 35° C. he represents his results for the mean specific heat from 
0° C. to f C. in terms of the mean calorie by the formula 
.V* = 0-99827-0-005184 (^/l00) + 0-006912(^/l00)2 
which gives a minimum at 35° C., agreeing with his observations. He points out 
that the coiTesponding formula for the specific heat at t, 
St = 0•99827-0•010368 (^/l00) + 0•020736 (^/l00)^ 
c 2 
