304 



On the Elasticity of Carbonic Acid Gas. 



papers which arc still in my hands. With respect to the employ- 

 ment of my formula by Ur. Joule and Dr. Thomson in their paper 

 " On the tiiermal Effects of Currents of Elastic Fluids " (Phil. 

 Trans. 1854)^ I have to state, that in May 1854, while my own 

 paper was unfinished, I communicated to those gentlemen a for- 

 mula for carbonic acid gas in which the value of a certain coeffi- 

 cient, denoted by PoVq, was stated at about y^^oth part less than 

 that which I afterwards found to be its correct value ; but that 

 difference is of no practically appreciable importance in compu- 

 ting the results of such experiments as those to which Dr. Joule 

 and Dr. Thomson applied the formula. 



I have the honour to be. Gentlemen, 



Your most obedient Servant, 

 Glasgow, March 1858, W. J. Macquorn Rankine. 



General Formula and Constants for Carbonic Acid Gas. 

 ZL_l_f. Jo 



P, pressure in lb. per square foot") at the absolute 



V, volume of one lb. in cubic feet J temperature t. 



(t= degrees above melting ice +274° C. 



To= 274° C). 



Pq= one atmosphere =2116'4 lbs. per square foot. 



Vq= 8'15725 cubic feet (volume which one lb. of car- 

 bonic acid would occupy at one atmosphere and 

 0° C. if it were a perfect gas. The actual volume 

 is 8-101 cubic feet). 



VoVq= 17264 foot-pounds. 



(PV for 0° and one atmosphere, actually = 17145 foot- 

 pounds). 



a= 1'9 for the Centiarade scale. 



Comparison with M. Regnault's experiments on the increase of 

 pressure at constant volume between 0° and 100° Centigrade. 



Let P'= pressure at 100° C. 

 Let P = pressure at 0° C. 



