MARTIN HEINRICH KLAPROTH {1743-1817) 

 JOHN DALTON {1766-1844) 



Gradually, and particularly by the work of such versatile, 

 learned, and energetic investigators as Scheele and Klaproth, 

 the experience accumulated by chemistry, concerning 

 the composition of the vast number of substances found 

 in nature or prepared experimentally, had arrived at the 

 point at which it was possible to distinguish as their com- 

 ponents a not very large number of fundamental substances, 

 out of which perhaps all other substances could be built up, 

 and which themselves were possibly of a simple nature, not 

 susceptible of further decomposition. An important matter 

 was the collection of extensive knowledge concerning the 

 weights of the fundamental components contained in various 

 compounds, or necessary to their formation, and in this con- 

 nection Klaproth especially did exemplary work. 



The assumption of the formation of all kinds of matter 

 from certain fundamental substances discovered by experi- 

 ment only became possible without inconsistency when 

 Black, Priestley, Cavendish, and again Scheele had shown 

 how seriously it was necessary to take the various kinds of 

 'air' - gases - which they had been the first to discover, as 

 weighable components; for the fundamental assumption was 

 the invariability in the weight of the components, whether 

 separate or in combination, and in however different a form. 

 Heat on the other hand, fire, (phlogiston) - however im- 

 portant it might be in preparing most substances, and hence 

 itself for long regarded as a necessary component - had 

 gradually been left out of these considerations; for it could not 

 be grasped by the balance. Lavoisier had in any case shown 

 that such a limitation in the number of the weighable funda- 

 mental substances made everything appear much simpler 

 than one had hitherto dared to think, and a simplification of 

 this kind has at all times been equivalent to the assurance 



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