1844.] of Bodies generally existing as Gases. 109 



the same time the part was filled with solid carbonic acid. It 

 melts at the temperature of 70 or 72 Fahr., and the solid 

 carbonic acid is heavier than the fluid bathing it. The solid 

 or liquid carbonic acid at this temperature has a pressure of 

 5'33 atmospheres nearly. Hence it is easy to understand the 

 readiness with which liquid carbonic acid, when allowed to 

 escape into the air, exerting only a pressure of one atmosphere, 

 freezes a part of itself by the evaporation of another part. 



Thilorier gives 100 C. or 148 Fahr. as the temperature 

 at which carbonic acid becomes solid. This however is rather 

 the temperature to which solid carbonic acid can sink by 

 further evaporation in the air, and is a temperature belonging 

 to a pressure not only lower than that of 5*33 atmospheres, 

 but even much below that of one atmosphere. This cooling 

 effect to temperatures below the boiling-point often appears. 

 A bath of carbonic acid and ether exposed to the air will cool 

 a tube containing condensed solid carbonic acid, until the 

 pressure within the tube is less than one atmosphere ; yet, if 

 the same bath be covered up so as to have the pressure of one 

 atmosphere of carbonic acid vapour over it, then the tempera- 

 ture is such as to produce a pressure of 2'5 atmospheres by 

 the vapour of the solid carbonic acid within the tube. 



The estimates of the pressure of carbonic acid vapour are 

 sadly at variance ; thus, Thilorier * says it has a pressure of 

 26 atmospheres at 4 Fahr., whilst Addamsf says that for 

 that pressure it requires a temperature of 30. Addams gives 

 the pressure about 27| atmospheres at 32, but Thilorier and 

 my self t give it as 36 atmospheres at the same temperature. 

 At 50 Brunei estimates the pressure as 60 atmospheres, 

 whilst Addams makes it only 34*67 atmospheres. At 86 

 Thilorier finds the pressure to be 73 atmospheres ; at 4 more, 

 or 90, Brunei makes it 120 atmospheres ; and at 10 more, or 

 100, Addams makes it less than Thilorier at 86, and only 

 62*32 atmospheres ; even at 150 the pressure with him is not 

 quite 100 atmospheres. 



I am inclined to think that at about 90 Cagniard de la 

 Tour's state comes on with carbonic acid. From Thilorier's 

 data we may obtain the specific gravity of the liquid and the 



Ann. de Chim. 1835, Ix. 427, 432. f Report of Brit. Assoc. 1838, p. 70. 

 J Phil. Trans, 1823, p, 193. Royal Institution Journal, xxi, 132. 



