6 Meldrum, Development of the Atomic Theory. 



reservations by W. C. Henry'" and Angus Smith", and by 

 Roscoe and Schorlemmer^' without objection. Owing to 

 the large circulation of Roscoe and Schorlemmer's book, 

 this version of the origin has decided the opinion of the 

 generality of chemists. There is, nevertheless, the best 

 reason for thinking that marsh-gas and olefiant gas did 

 not have the effect which it assigns to them of leading to 

 the theory. 



Indeed, in i8ii, Dalton connected the theory in its 

 early days with the oxides of nitrogen : — " I remember 

 the strong impression which at a very early period of 

 these inquiries was made by observing the proportion of 

 oxygen to azote, as i, 2, and 3, in nitrous oxide, nitrous 

 gas, and nitric acid, according to the experiments of 

 Davy."^° Thomson must have seen the necessity of aban- 

 doning the marsh-gas and olefiant gas story, for he said 

 in 1850 : — "Dalton founded his theory on the analysis of 

 two gases, namely, protoxide and deutoxide of azote." '■' 



Dalton's work on marsh-gas appears in the note-book 

 under date 6th August, 1804. Roscoe and Harden'^ point 

 out that he had been busily engaged on the theory the 

 year before. He had even arrived at the fundamental 

 ideas of his system, and had constructed a table of 

 atomic weights by September 6th, 1803. 



Obviously, Thomson's account of the origin of the 

 theory is untrustworthy, inasmuch as marsh-gas and 

 olefiant gas had no part in the matter. The question 

 arises, who is responsible for the error, Thomson or 

 Dalton ? Before answering this question it is necessary 



'" " Memoirs of DalLon," p. So. 



^ ' " Memoir of Dalton,"' p. 231. 



'- '• Treatise on Chemistry, Non-metallic Elements,'' p. 36, 1877. 



** Nicholsoiis Joiii-ii., vol. 29, p. I43, 181 1. 



' ■' Proc. Pliil. Soc. Glasgow, vol. 3, p. 140, 1850. 



1^ Op. cit., p. 28. 



