HEAT OF WATEE, WITH EXPERIMENTS BY A NEW METHOD. 
13 
Below 100° C. the uncertainty would probably not exceed 1 in 1,000, as the 
thermal capacity of the bulbs employed was only a quarter of that of the contained 
water. From 130° C. to 220° C. all the observations, except one at 130° C., were 
made with bulbs having a thermal capacity nearly equal to that of the contained 
water. In the observations at 100° C., 109° C., and 130° C., where both thick and 
thin bulbs were employed, the results deduced from the thick bulbs, assuming the 
same formula for the specific heat of quartz-glass, were systematically higher by 0‘12, 
0'17, and 0'23 per cent, respectively than those deduced from tlie thin bulbs. The 
point shown at 156° C. in fig. 1, which is the lowest depending entirely on observa¬ 
tions with the thick bulbs, shows so great an increase, when compared with 
Regnault’s ol)servations, as to suggest a systematic error of this kind. Assuming 
that the error might amount to OT per cent, in the mean specific heat at 100° C. with 
the thin bulbs, and that it would probably increase in proportion to the temperature 
and to the relative thermal capacity of the bulbs, it would amount to 0‘8 per cent, at 
200° C., which would be more than sufticient to bring the results of Dietebici into 
agreement with the most probable reduction of Regnault’s observations as indicated 
by my formula. A similar uncertainty would appjly with greater force to the 
experiments at higher temperatures where the thermal capacity of the quartz-glass 
bulbs amounted to four times that of the contained water. The heat-loss in 
transference might have been in part eliminated from the results for water by using 
the same hulbs full and empty at each temperature, but even in this case the accuracy 
of the results for water would have been reduced to about a fifth with the thickest 
bulbs. 
The large correction for the water ecpfivalent of the bulbs, which could not easily 
be reduced, is a serious objection to Dieteeici’s method as compared with Regnault’s 
at the higher temperatures. Below 100° C. this source of error is unimportant as 
compared with evaporation losses incurred in transferring hot water when exposed to 
evaporation, as in Ludin’s method. On this account there would probably be little 
hesitation in preferring Dieterici’s results to Luuin’s between 0° C. and 100° C., if 
it were not that, within the last year, Messrs. W. R. and W. E. Bouseield (‘ Phil. 
Trans. Roy. Soc.,’ A, 1911, vol. 211, pp. 199-251) have succeeded in reproducing 
Ludin’s results with remarkable fidelity by a method of electric heating with a 
vacuum-jacket calorimeter, which presents many ingenious and novel features. 
Owing to the uncertainty in the reduction of Dieterici’s results for the specific heat 
at 20° C., it might naturally be argued that his curve for the mean specific heat 
should be fitted to Ludin’s at a higher temperature, such as 60° C. or 70° C. This 
could easily be done by raising all the points representing Dieterici’s observations in 
fig. 2 by only 0'25 per cent., in which case .they would nearly aU agree with Ludin’s 
curve to 1 in 1,000 except those below 30° C., where Dieterici admits a larger 
possible error. It would then appear that Messrs. Bouseield, Ludin, and Dieterici 
were in fair agreement in assigning a much higher value to the mean specific heat 
