STANISLAO CANNIZZARO 149 



an element or compound wherein the properties of the element 

 or compound inhere, chemists would have at once been led 

 to a clear working description of the atom as the smallest 

 particle of an element in any molecule whereof the element 

 forms a part, and to the solution of the difficulty which stopped 

 Dalton. But the history of chemistry tells us that chemists had 

 to wait nearly half a century for the coming of a man of genius 

 to show them the real meaning of Avogadro's hypothesis, by 

 showing them how to use it as an elucidator of facts. That 

 man of genius was Stanislao Cannizzaro. 



The example and influence of Berzelius turned chemists 

 away from grappling with the difficulty that the Daltonian 

 theory left not overcome, to the ingathering of facts which bore 

 directly on the fundamental assumptions of the theory. Before 

 he received a copy of Dalton's book, Berzelius supposed that 

 the founder of the atomic theory must have based his con- 

 ception of chemical change, as interactions of atoms, on a 

 foundation of carefully verified facts. Berzelius indeed sup- 

 posed that Dalton had spent years in his laboratory amassing 

 facts concerning the compositions of diverse classes of com- 

 pounds, and had deduced from these facts the conclusion that 

 all elements and compounds interact chemically in the ratios 

 of certain constant and determinable quantities by weight, or 

 in the ratios of whole multiples of these quantities. Berzelius 

 saw that unless this statement were proved to be an accurate 

 presentation of facts, the Daltonian theory would have to be 

 abandoned. He therefore devoted himself for several years to 

 an experimental inquiry into the justness of what he supposed 

 to be the Daltonian law of chemical combination. When 

 Berzelius found, from a perusal of his book, that Dalton did not 

 state the fundamental facts of combination in the form of an 

 experimentally established law, but assumed the law as a 

 necessary deduction from the theory, he was more than ever 

 confirmed in his determination to make his criticism of the 

 Daltonian theory rest on work done in the laboratory, not in 

 the study. 



Other chemists followed the lines of inquiry laid down by 

 Berzelius ; and about ten years before the birth of Cannizzaro 

 the law of chemical combination . was firmly established by 

 accurate experimental v^'ork. For some 3^ears many chemists 

 almost abandoned the atomic theory. Proclaiming their deter- 



