THE ATOMIC VIEW OF NATURE. 



399 



actually the case. The lowest number according to which 

 any substance entered into combination with any other 

 was called the atomic weight or equivalent. 



There was, so far, no necessity to look upon atomic 

 weights as anything else than numbers fixing a propor- 

 tion. The unit could be selected arbitrarily. It was not 

 long before that element, hydrogen, which entered into 

 compounds in the relatively smallest weight was taken as 

 an arbitrary unit, and all other elements and compounds is. 



Equivalents. 



were tabulated according to the relative amount of their 

 weights required to form compounds with hydrogen or 

 with any other element e.g., oxygen the equivalent of 

 which with hydrogen was known. 1 



1 For many years after the enun- 

 ciation of the atomic theory great 

 uncertainty and much difference 

 of opinion existed on this and 

 other points. The man who did 

 most to elaborate tlie edifice of 

 which Dalton had laid the founda- 

 tions, who filled in the outlines and 

 invented the language of chemistry, 

 was Berzelius. He proceeded in- 

 ductively and gathered materials 

 from all sides ; to him are also 

 owing the greatest number of ac- 

 curate analyses, especially of inor- 

 ganic substances. When he began 

 his labours he was favourably dis- 

 posed towards Dalton's hypothesis ; 

 he clearly saw its capabilities, but also 

 that it was based only upon a happy 

 suggestion, that it was introduced 

 more by deductive than by induc- 

 tive reasoning, and that it needed 

 to be exhaustively tested and veri- 

 fied. After ten years, during which 

 he published in Gilbert's ' Annalen ' 

 and in Thomson's 'Annals of Philo- 

 sophy ' many series of investigations, 

 he was able in 1818 to publish, in 

 his ' Essay on Chemical Proportions 

 and on the Chemical Effects of 



Electricity ' (French translation, 

 1819 ; German translation, 1820), 

 the first systematic and complete 

 exposition of the atomic theory. 

 The beginning of a really exact 

 treatment of chemistry has been 

 dated by H. Rose, the greatest an- 

 alytical chemist of the century, from 

 this year 1818 the year in which 

 Dalton's hypothesis was proved 

 and generally accepted. Others 

 have dated the beginning from 

 1808, when Dalton published his 

 theory ; others again from 1776, 

 when Lavoisier destroyed the older 

 phlogiston theory and appealed to 

 the balance ; others again from 

 Black's discovery of latent heat in 

 1760. In an international history 

 of thought it is not of much in- 

 terest to decide whose claims to be 

 the founder of modern chemistry 

 as a science are best established. 

 Every one of these dates marks an 

 epoch in the advance of an im- 

 portant and independent branch of 

 research. Black took an important 

 step in the foundation of physical 

 chemistry through his introduction 

 of the conception of the quantity 



