1844.] of Bodies generally existing as Gases. 99 



nish to liquefy, but then the Indian ink stood. For further pre- 

 caution, an exact copy of the gauge was taken on paper, to be 

 applied on the outside of the condensing tube. In most cases, 

 when the experiment was over, the pressure was removed from 

 the interior of the apparatus, to ascertain whether the mercury 

 in the gauge would return back to its first or starting-place. 



For the application of cold to these tubes, a bath of Thilo- 

 rier's mixture of solid carbonic acid and ether was used. An 

 earthenware dish of the capacity of 4 cubic inches or more 

 was fitted into a similar dish somewhat larger, with three or 

 four folds of dry flannel intervening, and then the bath mixture 

 was made in the inner dish. Such a bath will easily continue 

 for twenty or thirty minutes, retaining solid carbonic acid the 

 whole time ; and the glass tubes used would sustain sudden 

 immersion in it without breaking. 



But as my hopes of any success beyond that heretofore ob- 

 tained depended more upon depression of temperature than on 

 the pressure which I could employ in these tubes, I endea- 

 voured to obtain a still greater degree of cold. There are, in 

 fact, some results producible by cold which no pressure may 

 be able to effect. Thus, solidification has not as yet been con- 

 ferred on a fluid by any degree of pressure. Again, that beau- 

 tiful condition which Cagniard de la Tour has made known, 

 and which comes on with liquids at a certain heat, may have its 

 point of temperature for some of the bodies to be experimented 

 with, as oxygen, hydrogen, nitrogen, &c., below that belonging 

 to the bath of carbonic acid and ether ; and, in that case, no 

 pressure which any apparatus could bear would be able to 

 bring them into the liquid or solid state. 



To procure this lower degree of cold, the bath of carbonic 

 acid and ether was put into an air-pump, and the air and gaseous 

 carbonic acid rapidly removed. In this way the tempera- 

 ture fell so low, that the vapour of carbonic acid given off by 

 the bath, instead of having a pressure of one atmosphere, had 

 only a pressure of ^th of an atmosphere, or ! inch of mer- 

 cury ; for the air-pump barometer could be kept at 8'2 inches 

 when the ordinary barometer was at 29*4. At this low tempe- 

 rature the carbonic acid mixed with the ether was not more 

 volatile than water at the temperature of 86, or alcohol at 

 ordinary temperatures. 



