From Alchemy to Chemistry:
Five Hundred Years of Rare and Interesting Books

University of Illinois at Urbana-Champaign
Rare Book Room Exhibit


CANNIZZARO, STANISLAO (1826 - 1910). Sunto di un Corso. Pisa, 1858.

Cannizzaro's lasting fame stems from a letter that he wrote in 1858 to a friend. This was the famous Sunto di un corso di filosofia chimica fatto nella Reale UniversitÓ di Genova, published in the journal Nuovo cimento and reprinted as a pamphlet in 1859. The complicated condition of chemistry that led Cannizzaro to compose his letter stemmed from events and personalities going back as far as fifty years before the Sunto appeared.

When Cannizzaro wrote the Sunto, there was no agreement among chemists as to what values should be adopted for atomic, molecular, or equivalent weights; no possibility of systematizing the relationship of the various elements; and no unanimity as to how organic compounds should be formulated. Cannizzaro began by stressing the distinction between atoms and molecules. He stressed that since all atomic weights are relative, one standard weight had to be chosen with which all other values could be compared. He chose hydrogen as this standard, but since he knew it to be diatomic, he used "half a molecule of hydrogen" as unity. Cannizzaro showed how vapor densities could be used to determine molecular weights (and atomic weights), and he laid to rest completely the idea that inorganic and organic chemistry functioned by different rules. As Tilden summed up his work in the Cannizzaro Memorial Lecture to the Chemical Society, "There is, in fact, but one science of chemistry and one set of atomic weights." It was Cannizzaro's recognition of true atomic weights that permitted Meyer and Mendeleev to formulate the periodic law at the end of the 1860's.

DSB; Partington IV, p489.


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