94 M. E. Wiedemann on the Specific Heats of Gases. 



The mean value is 02389, the greatest deviation from this 

 being 0*0025. 



Experiments Nos. 9 and 10 were carried out four weeks 

 after Nos. 1 to 8, and Nos 11 and 12 some time after 9 and 10 ; 

 during the earlier experiments the heating-vessel contained 

 boiling water ; during the two latter experiments it contained 

 melted paraffin. 



The numbers agree among themselves to as great an extent 

 as do those obtained by Regnault : thus he obtained numbers 

 varying from 0*23536 to 0*23890; my numbers vary from 

 0*2374 to 0*2414. The mean number 0*2389 obtained by me 

 differs by less than 1 per cent, from that obtained by Regnault, 

 viz. 0*23751. 



The method adopted for graduating the thermometer for 

 150° and 200° may fitly be described in connexion with the 

 specific heat of air. 



In order to determine the temperatures which corresponded, 

 in an air-thermometer, to the 150th and 200th degree of the 

 thermometer used in the heating-vessel, the paraffin-bath was 

 heated steady until the mercury column reached and remained 

 steadfast at the given degree. The process, as if for determi- 

 ning the specific heat of air, was then proceeded with ; and the 

 lowering of temperature of the air of the calorimeter was cal- 

 culated from the known specific heat of air (which, as shown 

 by Regnault, is independent of temperature) and from the 

 other data of the experiment. 



By adding this lowering of temperature to the mean tempe- 

 rature of the liquid in the calorimeter during the experiment, 

 which corresponds with the final temperature of the air after 

 cooling, the initial temperature of the air was obtained, and 

 therewith also the temperature measured by an air-thermo- 

 meter which corresponded with the position of the thermometer. 

 The differences of the calculated deviations of our thermome- 

 ters from an air-thermometer are of the same order as those 

 occurring in the estimation of specific heat itself. 



Hydrogen. 



The hydrogen was prepared from zinc and dilute sulphuric 

 acid in a Kipp's machine, purified by passing through caustic 

 potash, and dried by means of sulphuric acid. The following 

 Table expresses the mean specific heats obtained for hydrogen 

 between 100° and 20°. 



