dalton's first table of atomic weights. 269 



XXXV. Some Remarks on Dalton's First Table of Atomic 

 Weights. By Prof. Henry E. Roscoe, Ph.D., F.R.S. 



Read November 17th, 1874. 



As the Society is aware, the First Table, containing the 

 relative weights of the ultimate particles of gaseous and 

 other bodies, was published, as the 8th and last paragraph 

 to a paper by Dalton, " On the Absorption of Gases by 

 Water and other Liquids," read before this Society on 

 October 21, 1803, but not printed until the year 1805. 

 There appears reason to believe that these numbers were 

 obtained by Dalton after the date at which the paper was 

 read, and that the paragraph in question was inserted at 

 the time the paper was printed. The remarkable words 

 with which he introduces this great principle give us but 

 little clue to the methods which he employed for the de- 

 termination of these first chemical constants, whilst in no 

 subsequent publication, as in none of the papers which 

 have come to light since his death, do we find any detailed 

 explanation of how these actual numbers were arrived at. 

 He says* " I am nearly persuaded that the circumstance 

 [viz. that of the different solubilities of gases in water] 

 depends upon the weight and number of the ultimate 

 particles of the several gases, those whose particles are 

 lightest and single being less absorbable, and the others 

 more, according as they increase in weight and complexity. 

 An enquiry into the relative weights of the ultimate par- 

 ticles of bodies is a subject, as far as I know, entirely new. 

 I have been lately prosecuting this inquiry with remarkable 

 success. The principle cannot be entered upon in this 

 paper; but I shall just subjoin the results, as far as they 

 appear to be ascertained by my experiments." 

 • Manch. Mem. vol. i. 2nd ser. p. 286. 



