lo Meldrum, Dcvelopiiiciit of the Atomic TJicory. 



brilliant man than Davy, Thomas Thomson by name, 

 happening to get an account of the theory from Dalton 

 himself in the year iSo4,'\vas wise enough to see its 

 immense importance, and in the year 1807 gave an 

 admirable sketch of it in the 3rd edition of his "System 

 of Chemistry." Then in 1808 Dalton gave his own 

 version of it in the first instalment of his " New System 

 of Chemical Philosophy." Confirmation of the theory 

 had already appeared. At the beginning of the year 

 Tiiomson had published work on the oxalates of strontium, 

 and William Hyde Wollaston on the carbonates and 

 oxalates of potassium, which they each regarded as 

 exemplifying and justifying Dalton's teaching. This 

 work was of great importance at the moment. As 

 Wollaston remarked afterwards, " Chemists were by no 

 means duly impressed with the importance of this 

 observation of Dalton, until the}' were in possession of 

 other facts observed by Mr. Thomson and myself." -'■* 

 The historians of chemistry have failed to perceive the 

 full significance of this work. It refuted BerthoUet in a 

 specially telling way, for, in illustrating his doctrine, he 

 had made much use of acid salts of the kind that Thomson 

 and Wollaston examined. He had found them to be of 

 variable composition,-'" and now, in the light of Dalton's 

 theor)-, they were found to be perfectly definite substances. 



-'' Phil. Trans., y. 6, 1S14. 



"'* " Essai de Slatique Chimique,"' §§ 201 — 203 ; Mem. de fliisliiiit, 

 vol. 7, pp. 230 — 252, 297, 1806. Not only so, but Torbein Bergman 

 ("Dis.^ertation on Elective Attractions," § 9) and J. B. Richter (see report 

 by Karsten of a conversation with Kichtor, Allg.J. Chciiiic, (Scherer), 10, 

 1-38 — 143, 1803) thought that in many cases salts coulil be formed with a 

 decided superfluity of either ingredient. Further, it has been shown 

 recently (Joh. D'Ans, Zeilsch. anorg. Chein., 63, 225 — 229, 1909) that there 

 are four acid sulphates of potassium ; hence BerthoUet might well think that 

 these salts justified his belief in variable proportion: (see his Intro 'uction 

 to Riffault's translation of Thomson's " System of Chemistry," vol. i, p. 24.) 



