2 Mkldrum, Devclopvicut of the Atomic TJicory. 



sider, perhaps to realise for the first time, precise!}- what 

 their position is. Such was the case of the doctrine of 

 constant proportion. It seems to have arisen natnrall)' 

 and been taken for granted, assumed as a matter of 

 course, rather than considered and carefully defined. 

 Suddenly, about the beginning of the XlXth century, it 

 was called in question by Iierthollet. 



Primarily his teaching was concerned with the pro- 

 blems of chemical affinity. He had ample leisure to 

 meditate on the subject during his stay in Egypt, where 

 he had gone as an honoured member of the famous 

 Napoleonic expedition. The first fruits of that leisure 

 appeared in papers, read in Cairo before the shortlived 

 Institute of Egypt in June of the year 1799, in which he 

 propounded the valuable and original ideas of " mass- 

 action " and chemical equilibrium. Berthollet was thus 

 the founder of cJicuiical statics. Resuming the subject on 

 his return to France, he developed his ideas into a system 

 of chemistry, which is explained in various Memoirs' and 

 above all in his " Essai de Statique Chimique," (2 vols., 

 1803). 



His teaching aroused interest everywhere, witness the 

 appearance of English and German translations of his 

 works, and the extent to which his ideas permeated the 

 scientific dissertations'" and books of the period. His 

 main contention that chemical change was very largely a 

 matter of two factors, affinity and mass-action, could 

 hardly be denied. The tables of affinity which in the 

 course of the XVHIth century had become more and 



^ " Recherches sur les lois de I'Afiinite," MJni. de P Insliljit, vol. 3, 

 pp. I, 207, 228, 1801 ; vol. 7, 229, 1S06. 



'^ Memoirs, in which Proust, Thenard, Gay-Lussac, Avogadro, Berzelius, 

 and Dalton take BerthoUet's ideas into consideration will be cited as occasion 

 requires. A supplementary list of memoirs not specially referred to in this 

 paper, will be found in an appendix. 



