24 
PEOF. H. L. CALLENDAR ON THE VARIATION OF THE SPECIFIC 
A possible source of error to be carefully avoided in the continuous-mixture method 
is leakage of fluid at any point of the circuit between the first and last thermometers. 
Precautions against this were taken in designing the apparatus by making the 
cooling coils and other inaccessible parts of the apparatus of continuous lengths of 
solid-drawn tubing, and arranging all joints and connections as far as possible so as to 
be easily accessible and at all times open to inspection. 
In addition to this, a leakage test was regularly applied each day before starting 
observations, when the apparatus was at a nearly uniform temperature. The boiler 
was disconnected, and a glass tube of small bore was attached to the inflow at the 
top, to serve as an index. Any possible leaks were thus subjected to the full head of 
15 feet. A special test was also made for leakage between the hot and cold tubes in 
the exchanger. A small continuous leak due to strain, amounting to about 1 c.c. per 
hour, was detected on one occasion, and immediately rectified. But, as a rule, the 
movements of the sensitive index were negligibly small, being due merely to slight 
changes of temperature, and more often positive than negative. 
The apparatus was also tested with and without the jacket-tube J, figs. 4 and 5, 
between the exchanger and the regulator tank in which it was immersed. The loss 
from the thermometer-pockets, when unjacketed, was found to be from 1'2 to 1'4 
calories per second, according to the conditions of the experiment, and to be nearly 
independent of the flow, since the mean excess-temperature of the thermometer- 
pockets above the regulator tank, namely + + varied but slightly with 
the flow. The loss from the inner tubes of the exchanger itself, ivJien unjacketed, 
was nearly 2 calories per second, but varied by nearly 20 per cent, of itself when the 
flow was changed in the ratio of 1 to 10. This could easily be foreseen, because the 
cold current was raised to a higher temperature when the flow was small. The actual 
distribution of temperature in the outer tube of the exchanger was observed by means 
of thermocouples, and found to correspond with theory and with the observed changes 
in the heat-loss with flow. The jacket-tube J was designed to intercept this variable 
heat-loss and reduce it to about a tenth for the smallest flow. The mean rise of 
temperature of the jacket-tube for the smallest flow was found to be of the order of 
1° C. The mean difference of temperature between the jacket-tube and the regulator 
was always measured and allowed for in estimating the mean excess-temperature, but 
it was generally less than 0°‘2 C. for the largest flow, corresponding to a heat-loss of 
about 1 in 10,000, which was about the limit of agreement of the temperature 
measurements. It was ultimately, decided to do without jackets for the thermometer- 
pockets at temperatures below 100° C., because the heat-loss from the thermometer- 
pockets at these low temperatures was fairly small and nearly independent of the flow. 
The omission of these jackets considerably simplified the construction and connection 
of the apparatus. The main jacket J for the exchanger was employed in nearly all 
the experiments, because it made the heat-loss so nearly independent of the flow, and 
made the reduction of the observations comparatively simple and certain. 
