﻿320 Mr. Baly and Dr. Ramsay on the Relations of Pressure, 



We give one series of measurements together with the 

 values calculated from the known volume admitted: — 



Calculated. 



Found 



44 



4-2 



7-9 



r>-8 



9-4 



9-1 



9-1 



7-4 



11-9 



11-5 



16-7 



15-9 



21-2 



19-6 



These results are a further proof that the McLeod gauge 

 is of no value in determining the amount of rarefaction of 

 carbon dioxide. 



We also found it very easy to exhaust all hydrogen out of 

 the apparatus if there were any condensed carbon dioxide on 

 the containing walls. When the pump was started at about 

 10 millim. pressure, the spectrum of the gas in the vacuum-tube 

 was only that of hydrogen. As the exhaustion proceeded the 

 factor of exhaustion steadily increased while hydrogen slowly 

 disappeared from the vacuum-tube and carbon dioxide became 

 in evidence, till in a short time all the hydrogen had been 

 pumped out and only carbon dioxide remained. 



These facts may give an idea of the great difficulties we 

 met with in filling the apparatus absolutely with hydrogen. 

 This was a most lengthy and tedious operation. In spite of 

 the fact that the apparatus used for the hydrogen experi- 

 ments never had carbon dioxide put into it, the glass and the 

 phosphorus pentoxide nevertheless contained great quantities 

 of this gas condensed on them, the removal of which took a 

 very long time. First of all the apparatus was exhausted as 

 highly as possible and then the glass, especially the phos- 

 phorus-pentoxide tube, was raised to a high temperature 

 with a Bunsen-burner, the exhaustion being kept very high 

 in the meantime. Hydrogen was then admitted, and the 

 apparatus again exhausted, the heating being still continued. 

 This was repeated until no further carbon dioxide could be 

 brought off the walls by the heating in the vacuum and 

 until, after leaving it for a night, very highly exhausted, no 

 spectrum of carbon dioxide was visible in the vacuum-tube 

 when a current was passed. This process sometimes lasted a 

 fortnight. 



The foregoing results and the difficulties we met with in 

 filling the apparatus with hydrogen emphasize our criticism 

 on all previous work. For this fact of the condensation of 

 carbon dioxide does not appear to have been noticed by 

 previous experimenters. It would tend to make the read 



