88" M. E. Wiedemann on the Specific Heats of Gases. 



closing V and S, and the watch was read off. Then the tem- 

 peratures were noted for five to ten minutes — at first each 

 second, afterwards from minute to minute. A regular increase 

 of temperature occurred generally at the tenth and twentieth 

 seconds after closing the stopcocks; so short was the time 

 required for the temperature of the silver gauze to become 

 equalized with that of the water of the calorimeter. The 

 time was longer the higher the temperature of the entering 

 gas, inasmuch as the gauze situated nearest to the entrance- 

 aperture underwent a greater rise in temperature. Imme- 

 diately before and after the experiment the temperature of the 

 heating-vessel was determined, the mean of the two readings 

 being taken as the temperature during the experiment. 



Water maintained at the temperature of the air of the room 

 flowed continuously through the double-walled vessel -%. The 

 temperature of this water was determined before it entered 

 and when it flowed from %. Notwithstanding the wooden 

 screen, a slight increase in the temperature of the water was 

 observed ; the mean of the two readings was adopted. 



A, B, and C being again disconnected, B was reweighed ; 

 it had increased by the amount of water which had entered it. 

 Inasmuch as temperature and pressure remained constant 

 in B and C during the experiment, the volume of water (cal- 

 culated from the weight) which had entered B expressed the 

 volume of gas which had flowed from Q. It did not signify 

 whether diffusion had occurred through the caoutchouc balloon 

 or not ; if this did occur, it could only somewhat decrease the 

 purity of the gas. It was directly shown by experiment 

 (using carbonic acid and ammonia) that the gas in Q became 

 mixed with but traces of air. Although the water did not 

 possess the temperature of 4° C, the error arising from this 

 appeared so small as not to necessitate the use of a correction. 

 In order to calculate the weight of the issuing gas, it was 

 necessary that its temperature and pressure should be known. 

 The former was obtained, as has been already described, by 

 reading off the thermometer F. The latter was composed of 

 two parts — of the atmospheric pressure, and of the pressure 

 indicated by k. If the barometer-reading reduced to 0° be 

 represented by B, the reading of the manometer k reduced to 

 mercury be p, the temperature of the gas be .?, and the ob- 

 served volume of the gas be r, then the calculated volume at 

 0° and 760 millims. pressure is 



v -P + B 273 ' 2 

 ?0 '760" 273*2 +x V * 



If a represent the specific gravity. of the gas referred -to air. 



