Page:The Liquefaction of Gases.djvu/54

50 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 says it has a pressure of 26 atmospheres at -4° ., whilst says that for that pressure it requires a temperature of 30°. gives the pressure about 27 atmospheres at 32°, but and myself give it as 36 atmospheres at the same temperature. At 50° estimates the pressure as 60 atmospheres, whilst makes it only 34.67 atmospheres. At 86° finds the pressure to be 73 atmospheres; at 4° more, or 90°, makes it 120 atmospheres; and at 10° more, or 100°,  makes it less than 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° state comes on with carbonic acid. From data we may obtain the specific gravity of the liquid and the vapour over it at the temperature of 86° ., and the former is little more than twice that of the latter; hence a few degrees more of temperature