1880.] Physical Constants of Liquid Hydrochloric Acid. 121 



as it is evidently impossible to measure the relative volume of fluid 

 and gas within less than a fourth of a degree of the critical point, 

 and at this place the volumes are certainly unequal. This, however, 

 does not disprove their identity as the critical point. 



The density of the liquid at different temperatures was determined 

 in the same way as described in my former paper, and gave the 

 following numbers : — 



Temperature. Density. 



'908 



7-5 H73 



11-67 '854 



15-85 -835 



22-7 '808 



33-0 '748 



41-6 -678 



47-8 -619 



This liquid has therefore not quite such a high density as liquid car- 

 bonic acid, which is 95 at 0° C, and is about twice as high as acety- 

 lene, which is 0*450 at the same temperature. It is interesting to note 

 that acetylene is the lightest known fluid substance. On referring to 

 the density of liquid hydrochloric acid given by other authors, Pro- 

 fessors Roscoe and Schorlemmer, in their recent treatise on chemistry, 

 describe it as a colourless liquid having a specific gravity of about 

 1*27. As this value is so much higher than that obtained by myself, 

 and as I feel confident of the accuracy of my results, it seems evident 

 that a mistake has in some way arisen, and that the value given by 

 them refers to the density of the gaseous acid with reference to air, 

 and not to the liquefied gas. Unfortunately Faraday does not seem to 

 have determined its density. 



Experiments made to determine the coefficients of compressibility of 

 the fluid at different temperatures were carried on in the same way as 

 formerly detailed. The following are the chief results : — 



Mean coefficients of compression at different temperatures. Range 

 of pressure from 52 '8 to 208" 19 atmospheres. 



Temp, of HC1. 





Coefficient. 



47 -0 C. 





•00166 



41 -6 





•00123 



33 -0 





•00096 



22-7 





•000635 



15-85 





•00062 



10 -5 





•00054 



5-7 





•000397 



