THERMAL PROPERTIES OF CARBONIC ACID AT LOW TEMPERATURES. 375 



APPENDIX VII. 



Allowance for the Small Drop of Pressure in the \-inch Calorimeter ivhen used to 



Measure the Total Heat of the Gas. 



Let P be the point representing the condition of the gas entering the calorimeter, 

 and Q the point representing the gas leaving the calorimeter. PR is the constant- 

 pressure curve meeting the I curve through Q in II. Through Q draw a horizontal 

 cutting the pressure line in S. Let the drop of pressure in the calorimeter he dp. 



The amount of heat given to the gas = I (i I P = IH Ip- 



If there had been no drop of pressure in the calorimeter, this amount of heat would have 

 raised the gas to U instead of fl (i . The actual heat given is IK-!,., but to raise the tem- 

 perature to 0^ (or S ), if there were no throttling, we should have needed only I s I P . 



The heat may therefore be corrected by subtracting I u I s = rrdO = a (~7~) &P- '^' ie 

 " throttle correction " (Table A) is calculated in this way ; it is in all cases very small. 



PAPERS, &c., REFERRED TO. 

 Reference. 



(1) " Thermal properties of carbonic acid at low temperatures " by JENKIN and PYE, 



'Phil. Trans., Roy. Soc.,' Series A, vol. 213, p. 67 (1914). 



(2) MOLLIER, ' Zeit. fur die gesamte Kalte-Industrie,' Heft 4 and 5, pp. 65 and 



85, 1895. 



(3) AMAGAT, ' Annales de Chemie,' tome 29, 6th Series, 1893. 



(4) JOLY, 'Phil. Trans.' A, 1894, p. 943. 



(5) MOLLIER, ' Zeit. fur die gesamte Kalte-Industrie,' Heft 4, p. 65 (1896). 



(6) EWING, "The Mech. Production of Cold," 1908. The reference is to p. 195. 



(7) MOLLIER, ' Zeit. des Vereins Deutsch. Ingenieure,' 1904. 



