492 Sir W. Ramsay and Dr. B. D. Steele on the 



I should like, in conclusion, to express how much I have 

 been stimulated in the study of refraction by Professor Voigt, 

 in whose laboratory at Gottingen I made my preliminary 

 experiments on refraction in gases, and by Professor J. J. 

 Thomson, under whom the experiments were completed. For 

 their encouragement and advice in conversation and for their 

 published works I am very grateful. 



LX. The Vapour-Densities of some Carbon Compounds ; an 

 Attempt to Determine their correct Molecular Weights. By 

 Sir William Ramsay, K.C.B.^ F.R.S., and Bertram D. 

 Steele, D.Sc."^ 



[Plate XX.] 



THE accurate determination of the densities of gases has 

 been for long an object to which chemists have paid 

 attention. On the other hand, the density of vapours has 

 only been roughly estimated, as a means of arriving at a 

 conclusion regarding molecular weights ; whilst accurate 

 molecular weights have been deduced from the results of 

 analysis, and from previous determinations of atomic w^eights. 

 Every method which brings additional evidence to bear on 

 so important a class of constants as atomic weights must be 

 welcome ; and it was with great interest that the memoirs of 

 M. Daniel Berthelot were perused, " Sur la determination 

 rigour euse des poids moleculaires des gaz en partant de leurs 

 densites et de Fecart que celles-ci presentent par rapport a 

 la loi de Mariotte [Comptes rendus, 1898, xii. pp. 954, 1030, 

 1415, & 1501). In these papers M. Berthelot has brought 

 Regnauit's determinations of the compressibility of hydrogen, 

 nitrogen, oxygen, and carbon monoxide between one and six 

 atmospheres to bear on determinations of their density by 

 M. Leduc, in such a manner that their relative weights can 

 be compared when, if Avogadro^s hypothesis be granted, 

 equal volumes contain equal numbers of molecules. In the 

 case of the elementary gases, oxygen, hydrogen, and nitrogen, 

 inasmuch as the molecules are diatomic, the determination of 

 the molecular weight is at the same time a determination of the 

 atomic weight; and with carbon monoxide the atomic weight 

 of carbon is arrived at by simple subtraction. To quote 

 Berthelot'' s words : ^' Le volume moleculaire d'un gaz a 0° et 

 sous la pression atmospherique etant egal a 1 pour un gaz 

 qui suivrait exactement la loi de Marriotte, ce volume a la 

 valeur 1 — a pour un gaz qui ne la suit pas.''' The definition 



* Communicated by tlie Physical Society : read December 12, 1902. 



