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DETERMINATION OF THE Ratio oF SpeciFic Heats or Dry Arr. 
BK. K. CHAPMAN. 
The following method for determining the ratio of specific heats was 
suggested by some work in connection with an experiment in a fog chamber. 
It became necessary to know the temperature in a fog chamber on sudden 
expansion and consequent condensation of vapor. In order to measure this 
temperature a thermo-couple of Cu and Fe was introduced, and the deflec- 
tion of a galvanometer connected in series with the couple was noted on 
the expansion of the saturated vapor. The couple was then graduated by 
keeping one junction at a constant temperature and noting the deflection 
of the galvanometer for a given change in temperature of the other junc- 
tion. Knowing, then, the constant of the apparatus, the temperature in the 
fog chamber was easily determined. 
The attempt was then made to use this method for finding the tem- 
perature in a chamber of air on sudden expansion, and thus determine the 
ratio of the specific heats. 
To the stopper of a glass carboy was fitted a large valve that could 
readily be opened or closed by hand. One junction of the thermo-couple 
was introduced into the carboy through a rubber stopper fitted in a hole 
drilled in the side. The inner ends of the bent tube carrying the couple 
were then separated by twisting the tubes in the rubber stopper. The other 
junction was encased in a small glass bulb just outside the bottle and this 
kept at a temperature of the surrounding medium. Later in the work 
the entire apparatus, excepting the valve, was immersed in a bath which 
could be maintained at a constant temperature. Dry air was then pumped 
into the bottle and the whole was allowed to stand until it had regained 
the temperature of the surroundings. On opening the valve the temperature 
falls, due to the adiabatic expansion, and the galvanometer is deflected 
because of the difference in temperature of the two junctions of the couple. 
From this deflection it was hoped that the lowest temperature in the cham- 
ber might be calculated. A great deal of difficulty was experienced in try- 
ing to calibrate the couple, since the deflections due to a given difference 
in temperature varied considerably, and the degrees of accuracy desired 
[1926988] 
