BETWEEN ONE ATMOSPHERE AND HALF AN ATMOSPHERE OF PRESSURE. 371 



founded on CHAPPUIS' measures and applicable at C. The unit of pressure is hen 

 the atmosphere. According to this, for p = 1 we get pr = 1 -00665, as compared 

 with / = 1 for i" = QO j in close agreement with my value recorded ahove. 



A comparison of CHAPPOTS' method and apparatus with mine may not be without 

 interest. On his side lay a very considerable advantage in respect of the " nocuous- 

 space" V s , inasmuch as this was reduced to as little as Tl cub. centims., whereas mine 

 was ten times as great. The advantage would be important when working at 

 temperatures other than that of the room. Otherwise, the influence of V, did not 

 appear to prejudice my results, except in so far as V 3 might be uncertain from 

 capillarity in the manometer ; and this cause of error would operate equally in 

 CHAPPUIS' apparatus. 



So far as a 2 : 1 ratio suffices, my method of varying the volume seems the better, 

 and, indeed, not to admit of improvement. 



In the manometric arrangements it would seem that both methods are abundantly 

 accurate, so far as the readings are concerned. I am disposed, however, to favour a 

 continual verification of the vacuum by the To'pler pump, and, what is more important, 

 a method of reading which is independent of possible errors arising from irregular 

 refraction at the walls of the manometric tubes. 



It may be remarked that, with a partial exception in the case of CO.,, 

 M. CHAPPUIS' work relates to pressures rtbore atmosphere. 



Other papers which have appeared since my Preliminary Notice are those of 

 M. GUYE, working both alone and with the assistance of collaborators.* Several of 

 these relate to the atomic weight of nitrogen and insist on the discrepancy between 

 the number resulting from density and that of STAS. Among the methods employed 

 is that of decomposing nitrous oxide by an incandescent iron wire and comparing 

 the original volume with the residual nitrogen. In my handst this method failed to 

 give good results, in consequence, apparently, of the formation of higher oxides of 

 nitrogen. 







P.S., March 6. Some observations upon Ammonia may here be appended. The 

 gas was evolved (almost without warmth) from the solution in water, and was dried 

 by very slow passage over fragments of caustic potash. The precautions mentioned 

 under nitrous oxide were here followed with more minute care. The glass surfaces 

 were in contact with the gas for weeks, either at half atmospheric or whole 

 atmospheric pressure, and the observations at full pressure were not commenced 

 until that pressure had prevailed for a day or more. On the reduction of pressure 

 to the half atmospheric, ammonia was sensibly liberated from the walls, and perhaps 

 from the cement in the manometer. In the observations to be compared, the same 



* 'C. R.,' April 25, May 16, June 13, July 4, October 31, 1904. 

 t ' Roy. Roe. Proc.,' vol. 62, p. 204, 1897 ; ' Scientific Papers,' vol. 4, p. 350. 



3 B 2 



