100 On the Liquefaction and Solidification [184-4. 



In order to obtain some idea of this temperature, I had an 

 alcohol thermometer made, of which the graduation was carried 

 below 32 Fahr., by degrees equal in capacity to those between 

 32 arid 212. When this thermometer was put into the bath 

 of carbonic acid and ether surrounded by the air, but covered 

 over with paper, it gave the temperature of 106 below 0. 

 When it was introduced into the bath under the air-pump, it sank 

 to the temperature of 166 below 0; or 60 below the tempera- 

 ture of the same bath at the pressure of one atmosphere, i. e. in 

 the air. In this state the ether was very fluid, and the bath 

 could be kept in good order for a quarter of an hour at a time. 



As the exhaustion proceeded I observed the temperature of 

 the bath and the corresponding pressure at certain other 

 points, of which the following may be recorded : 



The external barometer was 29*4 inches : 



inch. Fahr - 



when the mercury in the air-"\ , ' the bath tempe-l __JQ^ 



pump barometer was. . / rature was. . j 



33 > 33 33 t) )> 33 ***lj 



t3 33 33 33 6\) 33 33 33 I 



99 



j> 39 39 99 39 "6 33 it it 



tt 99 3 i) ^ a 93 39 



9(\ 



J> 33 99 ^ U 99 J) 33 



97 



t) )> >J 33 33 ~* 33 33 39 



9S 

 J> J> 33 33 33 33 



9R'9 

 i> JJ 33 33 **<3 A ,, ,, ,, 



but as the thermometer takes some time to acquire the tempera- 

 ture of the bath, and the latter was continually falling in degree ; 

 as also the alcohol thickens considerably at the lower tempera- 

 ture, there is no doubt that the degrees expressed are not so low 

 as they ought to be, perhaps even by 5 or 6 in most cases. 



With dry carbonic acid under the air-pump receiver I could 

 raise the pump barometer to 29 inches when the external 

 barometer was at 30 inches. 



The arrangement by which this cooling power was combined 

 in its effect on gases with the pressure of the pumps, was very 

 simple in principle. An air-pump receiver open at the top was 

 employed ; the brass plate which closed the aperture had a 

 small brass tube about 6 inches long, passing through it air- 

 tight by means of a stuffing-box, so as to move easily up and 



131, 



