STANISLAO CANNIZZARO i59 



the equivalency of atoms, following from the same study, 

 Cannizzaro uses these laws in the examination of " the trans- 

 formations of matter," which he says is " the true object of 

 our science." He classifies reactions, and expresses them in 

 general formulas, using the symbols R', R", R'", etc., to denote 

 monatomic, diatomic, triatomic, etc. (or, as they are now called, 

 univalent, bivalent, tervalent, etc.), atoms, and radicles — that is, 

 according to Cannizzaro, atomic groups which function as simple 

 atoms in particular interactions. 



Cannizzaro's method of studying interactions was to con- 

 sider particular cases in detail, and then to generalise these in 

 symbolic expressions, which included all the special interactions 

 he had examined, and suggested others. He investigated direct 

 combinations of simple and compound radicles ; substitutions of 

 simple and compound radicles in chlorides, bromides and 

 iodides; substitutions of radicles in acids, and in salts; double 

 exchanges of the radicles, classified in accordance with their 

 saturation-capacities, in the interactions of pairs of compounds. 

 In studying these transformations of matter, Cannizzaro brings 

 out unlooked-for analogies between the metals of inorganic, and 

 the radicles of organic chemistry ; he develops the conception 

 of substitution, and makes clear what Dumas dimly saw when 

 he spoke of "the maintenance of chemical type"; he classifies 

 acids in accordance with their basicities, and shows, by ex- 

 amples, the usefulness of this classification ; he removes the 

 difficulties about oxy-acids and hydro-acids which had been 

 troubling chemists since the time of Lavoisier ; he develops 

 and uses consistent formulas for both inorganic and organic 

 compounds, formulas which include and reconcile the con- 

 ceptions sought after by Dalton, Davy, Berzelius, Gerhardt, 

 Laurent, Dumas, Liebig, and many other chemists of renown. 



All this, and more than this, was the goodly gift that 

 Cannizzaro gave to chemists more than half a century ago, at a 

 time when all other chemists were groping in the jungle of 

 facts, and almost despairing of a way out. Cannizzaro did not 

 show chemists a way out of the jungle of facts ; he showed them 

 how to bring order into the facts. Get out of the sensible 

 realities, and you are lost ; remain in the realities without 

 guiding ideas, and you are lost too. The illuminating, con- 

 trolling, order-producing, fruitful conception was near at hand ; 

 but no one seized it until Cannizzaro came. 



