LECTURE IV.] HISTORY OF CHEMISTRY. 53 



necessary to determine the proportional quantities of one acid 

 against the different alkaline bases ; afterwards, it is sufficient 

 to ascertain the proportional quantity of a single compound of 

 every other acid with one alkaline basis, when, by means of an 

 easy calculation, the proportional quantities of the acids in all 

 the other compounds may be determined." It may be said, 

 indeed, that Fischer's table was the first table of equivalents. 

 The numbers attached in it to the different bases, represent 

 equivalent quantities, since these quantities are neutralised by 

 the same quantity of acid ; and conversely with respect to the 

 different acids. The conception of the equivalent was, in this 

 way, established about the year 1803, although the word itself 

 was not in use at that time. The discovery of the law of 

 multiple proportions, and the formulation of the atomic theory 

 by Dalton (which were first announced in the third edition of 

 Thomson's System of Chemistry), both took place almost at 

 this same time. 



I wish to deal, in a few words, with the questions of priority 

 which were called forth by these important experiments and 

 views. 15 The idea of the atomistic point of view is an old one, 

 and at the beginning of this lecture I have named a few Greek 

 philosophers who advanced and upheld the theory. The 

 opinions pass down through all the centuries ; they are con- 

 tested ; but they always find supporters. The chemists of the 

 eighteenth century appear to have embraced pretty generally 

 the atomistic way of regarding matter. I may here adduce the 

 views of Lavoisier with respect to the constitution of matter, 

 which I have already stated at length ; and those of Berthollet, 

 who frequently speaks of molecules. In one word, these were 

 the opinions of the day, and they were preferred to the dynamic 

 hypothesis, chiefly, it is almost certain, because the assumption 

 of discreet particles of matter, separate from one another, fur- 

 nished a simple explanation of the diminution of volume with 

 the lowering of temperature. 



Dalton, on his part, did not claim that he had introduced 



15 Compare the work by Smith, already mentioned. 



