ATOMIC WEIGHTS. 



THE study of the quantitative relations between reacting 

 substances was begun long before Dalton announced 

 his atomic theory which did so much to explain them. 

 Centuries before the time of Dalton an atomic theory had 

 been advanced to account for the physical properties of 

 substances from which his theory differed in many ways, 

 although in many points there was a striking similarity. 

 Dalton's theory sprang from the necessity of finding an ex- 

 planation of facts derived from experiments and it dealt with 

 much smaller particles than the ancient theory. The new- 

 theory was a chemical, the old a physical one. Dalton was 

 not contented with a mere statement (i) " that the ultimate 

 particles of all homogeneous bodies are perfectly alike in 

 weight, figure, etc. In other words, every particle of water 

 is like every other particle of water ; every particle of hy- 

 drogen is like every other particle of hydrogen, etc." He 

 went further and attempted to determine the relative weights 

 of these ultimate particles of various elements and com- 

 pounds. His success in this department of research was 

 not great, and what astonishes us is that with such analytical 

 results he should have enunciated his theory so clearly and 

 comprehensively as he did. Of those who worked in this 

 field of research one name stands out far above all others. 

 Not only for the accuracy of his experimental work, but also 

 for the many ingenious processes and reactions which he 

 employed to arrive at his goal, will the name of Berzelius be 

 ever honoured. Besides these determinations of theoretical 

 interest, the new theory led to an enormous advance in the 

 accuracy of all quantitative analysis, for it is obvious that 

 now one had a standard far more infallible than a mere com- 

 parison with the results obtained by other chemists by which 

 one could test the accuracy of analytical processes. 



Speculative chemists and physicists tended to go still 

 further back than to the atoms, for, they asked, are not 

 atoms made of something and may not that something be a 



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