Table 225. 



COEFFICIENTS OF THERMAL EXPANSION. 



Coefficients of Expansion of Oases. 



The numbers obtained by direct experinu nt mi tic clianj;e of volume at constant pressure, Ep, are separated in the 

 table from those obtained from the clianee of pressure at constant volume, Ev The two parts of the table are 

 headed " Coefficient at constant pressure '' and " Coefficient at constant volume," respectively. Ordinary changes 

 of atmospheric pressure produce very little chance in the coefficient of expansion, and hence entries in the pressure 

 colunni of i atm. have been made for all pressures near to 76 centimetres of mercury. The other numbers in the 

 pressure columns are centimetres of mercury at o C. and approx. 45° latitude, unless otherwise marked. 



Thomson has given (vide Encyc. Brit. art. "Heat") the following equations for the calculation of the expan- 



sion, E, betrt'een 

 constant pressure. 



o"^ and loo*^ C. of the gases named. 

 Hydrogen 



E = 



Common air . 

 Oxygen . . . 

 Nitrogen . . 

 Carbon dioxide 



Expansion is to be understood as change of volume under 



.3662 ( I — .00049 — " ) 



.3662(1 + .0026 —A 



.3662 f I -f .0032 ^\ 

 ^ Va' 



.3662(1 +.0031 K°\ 



.3662(1 + .0164 —A 



where V^ / Vo is the ratio of the actual density of the gas at 0° C. to the density it would have at 0° C. and one 

 atmosphere of pressure. The same experiments (Thomson & Joule, Trans. Roy. Soc. i860), — which, together 

 with Kegnault's data, led to these equations, — give for the absolute temperature of melting ice 2.731 times the 

 temperature interval between the melting-point of ice and the boiling-point of water under normal atmospheric 

 pressure. 



* Corrected by MendelejefF to 45° latitude and absolute expansion of mercury. Rowland gets almost the same 

 correction on Rcgnault, using Wiillner's value of the expansion of mercury. 



t The series of results at different pressures are given because of their interest. The absolute values are a little 

 too low. (See preceding footnote.) 



Smithsonian Tablcs. 



218 



