158 



DR. FARADAY ON THE LIQUEFACTION AND SOLIDIFICATION OF 



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 temperature 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 -g^th of 

 an atmosphere, or 1*2 inch of mercury; for the air-pump barometer could be kept 

 at 28'2 inches when the ordinary barometer was at 29*4. At this low temperature 

 the carbonic acid mixed with the ether was not more volatile than water at the 

 temperature of 86°, or alcohol at ordinary temperatures. 



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° and 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 

 temperature of the same bath at the pressure of one atmosphere, /. 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 tim.e. 



As the exhaustion proceeded I observed the temperature of the bath and the corre- 

 sponding pressure, at certain other points, of which the following maybe recorded: — 

 The external barometer was 29*4 inches : 



inch. Fahr, 



o 



when the mercury in the air-pump barometer was 1 the bath temperature was— 106, 



10 

 20 



22 

 24 

 26 



27 

 28 

 28-2 



-112i, 



— 121, 



— 125, 



— 131, 

 -139, 



— 146, 



— 160, 



— 166; 



but as the thermometer takes some time to acquire the temperature of the bath, and 

 the latter was continually falling in degree ; as also the alcohol thickens considerably 

 at the lower temperature, 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 baro- 

 meter to twenty-nine inches when the external barometer was at thirty inches. 



