HEAT OF WATER, WITH EXPERIMENTS BY A NEW METHOD. 
23 
lower than Ludin’s, but the discrepancy here is only from 0°‘043 C. to 0°’065 C. 
They considered that the measurements could not be carried beyond this point with 
an open calorimeter owing to the rapidly increasing uncertainty of the lieat-loss due 
to evaporation, “obturator” heating, &c. The general agreement with Ludin’s curve 
is so striking that it would seem at first sight as though it could hardly be due to 
chance. Their methods had no points in common, except that they both used 
mercury thermometers and open calorimeters. 
Reduction of Observations by the Total-Heat Method. 
The curves of variation of total-heat above described and explained, when plotted 
on a scale of 1 mm. to 0°’001 C. for dh, atforded the most accurate and expeditious 
method of reducing the observations by the continuous-mixture method, since it was 
easy to take exact account in this way of small differences of range with different 
flows. If /?i, /? 2 , hs, Ih are the total heats from 0 ° C. corresponding to the observed 
temperatures b; L) L) equation (7), when expressed in terms of the total heat, 
becomes 
< Ih — ^h = Ih—k-i + X/Q .(ll) 
Substituting k = t + dh, and writing Xt for the sum b"L + ^. 3 —L) and 'Edh for the 
sum dhi — dh 2 + dhr^—dhi, this equation may be written 
Q (2^-l-2db) = X.(12) 
If the formula assumed for dh is correct, the values of the heat-loss X deduced from 
different flows should be nearly the same for the same temperature range, or should 
vary in relation to the mean excess-temperature of the calorimeter above its 
surroundings. If the formula employed for dh is incorrect, the calculated values of 
the heat-loss X will vary with the flow, and will bear no consistent relation to the 
external conditions. 
As there was some delay in procuring the requisite sizes of solid-drawn copper tube 
for the high-pressure apparatus designed for work at temperatures up to 230° C., the 
appai’atus was in the first instance constructed of ordinary brass tubing with solder 
joints for work below 100 ° C. The soft-solder joints would not stand high tempe¬ 
ratures, but had the advantage that the apparatus could be taken to pieces I'eadily 
and remade in different forms, to test the effect of variations in the external 
conditions on the heat-loss observed. Thus in order to test for possible errors due to 
conduction of heat along the thin tubes, 2 to 3 cm. long, 5 mm. bore, and 0'5 mm. 
thick, connecting the thermometer-pockets to the exchanger, the connecting tubes 
were replaced by short thick brass cylinders 1 cm. long by 2 cm. in diameter. This 
produced an appreciable effect on the thermometer readings only with the smallest 
flow of 1’25 gr./sec. It was inferred that the conduction error with the thin tubes 
actually employed would be inappreciable even with the smallest flow. 
