108 



On the Liquefaction and Solidification [1844. 



Fahr. below 0, and is then a white, crystalline, translucent sub- 

 stance, not remaining clear and transparent in the solid state 

 like water, carbonic acid, nitrous oxide, &c., but forming a 

 mass of confused crystals like common salt or nitrate of am- 

 monia, solidified from the melted state. As it fuses at tempe- 

 ratures above -122, the solid part sinks freely in the fluid, 

 indicating that it is considerably heavier. At this temperature 

 the pressure of its vapour is less than one atmosphere not 

 more, probably, than 0'8 of an atmosphere, so that the liquid 

 allowed to evaporate in the air would not solidify as carbonic 

 acid does. 



The following is a Table of the tension of its vapour, the 

 marked numbers being close to experimental results, and the 

 rest interpolated. The curve resulting from these numbers, 

 though coming out nearly identical in different series of experi- 

 ments, is apparently so different in its character from that of 

 water or carbonic acid, as to leave doubts on my mind respecting 

 it, or else of the identity of every portion of the fluid obtained, 

 yet the crystallization and other characters of the latter seemed 

 to show that it was a pure substance. 



Carbonic Acid. The solidification of carbonic acid by M. 

 Thilorier is one of the most beautiful experimental results of 

 modern times. He obtained the substance, as is well known, 

 in the form of a concrete white mass like fine snow, aggregated. 

 When it is melted and resolidified by a bath of low tempera- 

 ture, it then appears as a clear, transparent, cystalline, colour- 

 less body, like ice; so clear indeed, that at times it was 

 doubtful to the eye whether anything was in the tube, yet at 



