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 temperature 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[1] says it has a pressure of 26 atmospheres at -4° Fahr., whilst Addams[2] says that for that pressure it requires a temperature of 30°. Addams gives the pressure about 2712 atmospheres at 32°, but Thilorier and myself[3] give it as 36 atmospheres at the same temperature. At 50° Brunel[4] 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°, Brunel 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 vapour over it at the temperature of 86° Fahr., and the former is little more than twice that of the latter; hence a few degrees more of temperature
