

,.|;<)F. f. FKKWEX JENKIN AND MB. D. R. PYE ON THE 



,;. j,,i,,te between the steel tubes and the vulcanite pieces were perfectly tight 

 UII1 |,. r tl..< maximum pressure used, 900 Ibs. per sq. in. The bore of the valve ,s 

 ,', in,-!, diameter and the passages are t)ell-mouthed oa both sides. A plug formed 

 of rolled copper gauze serves to dissipate the kinetic energy of the jet issuing from 

 the valve. The time occupied in the passage from one thermo-junction to the other, 

 at the slowest rate of flow, was only a fraction of a second. 



The thermo-junctions were connected to the selector switch (p. 85) in such a way 

 that the temperature of either junction, or the difference between the two, could be 

 measured. The latter arrangement was convenient, since it was the difference of 

 temperature which was being investigated. 



Before using the new apparatus tests were made to ascertain whether the heat 

 insulation was in fact perfect, and also what difference, if any, there was between the 

 readings of temperature given by the two thermo-junctions. The construction of the 

 apparatus makes these tests very simple. 



To avoid the slightest drop of pressure between the thermo-junctions, a simple full- 

 bore block of vulcanite (also shown in fig. 16) was substituted for the adjustable valve, 

 then liquid COj was passed through the apparatus, first with the thermo-junctions in 

 their normal positions, and again when the thermo-junctions had been interchanged, 

 end for end. The apparent difference of temperature between the thermo-junctions 

 in the first case represents the sum, and in the second case, the difference, of the two 

 quantities to be determined, viz., the actual change of temperature of the liquid and 

 the difference of the thermo-junctions. 



Experiments were made with liquid C0 a at temperatures ranging from + 20 C. to 

 50 C. They showed that there was no change in the temperature of the liquid, 

 but that there was a very slight difference between the thermo-junctions. This was 

 allowed for in subsequent measurements.* As a further check, similar tests were 

 made with wet CO, vapour instead of liquid C0 2 . The difference between the 

 readings of the thermo-junctious was confirmed. There could be no difference of 

 temperature of the vapour in this case, since the pressure was the same at the two 

 junctions. 



As the calorimeter could not be cooled much below 40 C., and readings were 

 wanted at 50 C., an " infra-cooler" was inserted in the pipe between the calori- 

 meter and the throttle valve, by which the liquid could be cooled to any extent 

 desired. By this means readings were obtained down to -55 C. The " infra-cooler " 

 consisted of two concentric copper pipes 10 feet long, the inner one inch external 

 diimu-ter, the outer one f inch internal diameter. The liquid C0 2 passed through the 

 inner tube, while a separate supply of liquid C0 2 was admitted to the outer tube and 

 evaporated at a pressure of about 80 Ibs. per sq. in., escaping through a throttle valve 

 ato the atmosphere. The concentric pipes were bent into a coil about 9 inches 

 diameter and well lagged with cotton wool The arrangement worked well, though 



* See note on Table V. 



