A CENTURY OF CHEMISTRY. 81 



the laboratory or found in nature. In 1802 Fischer 

 made the first table of " chemical equivalents," show- 

 ing what quantities of the different alkaline bases are 

 neutralised by the same quantity of an acid, and con- 

 versely for the acids. 



But while it is important even in a short historical 

 sketch to observe that scientific discoverers have very 

 rarely a Minerva birth, we must not obscure the fact 

 that though Richter, Proust, and others were work- 

 ing towards a big conclusion, it is to John Dalton 

 that we are indebted for the clear statement of 

 the fundamental fact regarding chemical combina- 

 tion: that substances, both simple and compound, 

 always combine in definite proportions of their 

 weights. In whatever way one substance is trans- 

 formed into another, the masses of the two substances 

 always bear a fixed ratio. Even if several substances 

 react together, their masses and those of the new 

 bodies are always in fixed proportions. These facts 

 almost necessarily lead to the atomic conception. 



Dalton. The doctrine of the Quaker chemist de- 

 pended partly on the following results of experi- 

 ence : 



" Ko new creation or destruction of matter is with- 

 in the reach of chemical agency. We might as well 

 attempt to introduce a new planet into the solar sys- 

 tem, or to annihilate one already in existence, as to 

 create or destroy a particle of hydrogen " (Dalton, 

 after Lavoisier). 



In a chemical compound the different constituents 

 are always present in invariable proportions (Dal- 

 ton, after Proust). 



In the interactions of acids and bases, etc., the 

 quantity by weight of an element, or of a compound 

 which takes active part in the chemical change is al- 



