104 CHEMICAL DISCOVERY AND INVENTION 



For such a statement, if we make allowance for a little exag- 

 geration arising out of not unnatural national pride, justification 

 would be sought in the interpretation of the facts then accumu- 

 lated about combustion and the overthrow of the then prevalent 

 doctrine of " phlogiston " which science owes to the genius of 

 Lavoisier. The classification of acids, bases, and salts, and the 

 system introduced in his remarkable Traite elementaire de 

 Chimie, as well as the nomenclature which in principle is used, 

 so far as it is applicable, down to the present day were also 

 part of his work. 



By some English writers, on the other hand, John Dalton in 

 virtue of his " Atomic Theory " has been regarded as the real 

 founder of the modern science. For this view there is some 

 justification, for the conception introduced by Dalton in 1808 

 remains to this day the indispensable foundation on which all 

 modern chemistry is built, and without which some departments 

 of our science, notwithstanding the accumulation of facts, would 

 either not exist at all, or would remain a chaotic assemblage of 

 observation and hypothesis. 



Whatever may be the verdict about the claims of these older 

 men of science as founders of modern chemistry there have been 

 undoubtedly epochs from which a new departure may be dated. 

 One of these, inaugurated about 1860, arose out of the belated 

 recognition of a principle enunciated clearly enough fifty years 

 before by the Italian physicist Avogadro. 



It was a countryman of his, Cannizzaro, for the last forty 

 years of his life professor of chemistry in the Royal University of 

 Rome, who with remarkable insight perceived the importance of 

 Avogadro's hypothesis, and w r ith most praiseworthy insistence 

 persuaded the chemical world of 1858 to listen to his expositions. 

 The principle will be explained a little later. 



About this time also began the more systematic study of the 

 physical properties of substances in connection with the enquiry 

 into their composition which had been previously the chief 

 business of the chemist. The melting points, the boiling points, 

 the specific gravities, the optical properties of bodies hence- 

 forward occupied attention, and it was by observations of one 

 of these properties, namely, the power possessed by many 

 substances of rotating the plane of polarisation of a ray of 

 polarised light, that one of the most fruitful discoveries of our 

 time was made. The first observations on the fact that for 



