MODERN SCIENCE. 183 



but in unequal degrees, strongly positive atoms showing 

 affinity for negative atoms, and conversely : thus establishing 

 (for a time) his views of the dual structure of chemical 

 compounds a doctrine partly overthrown by Dumas's 

 unitary theory. By the application of a few rules regarding 

 the combinations of elementary atoms, he extended the 

 bounds of the atomic theory of Dalton : established the 

 fact that the same laws of combination, the same fixity of 

 composition, and the same general features of atomic struc- 

 ture prevail among the so-called organic as among the 

 inorganic compounds, thereby removing the barrier which 

 separated the two branches. He will be remembered beyond 

 all things, however, for his determination of ATOMIC WEIGHTS 

 an investigation which demanded an amount of labour, 

 perseverance, patience, and working power of which those 

 who are unacquainted with the detail of experimentation 

 have no idea. 



17851838. Dulong discovered CHLORIDE OF NITROGEN, 

 a powerful explosive ; in collaboration with PETIT discovered 

 THE LAW, " The atoms of all solid elements have the same 

 capacity for heat" thus putting a most important generalisa- 

 tion in the hands of the chemist ; since guided by it, 

 together with Mitscherlich's law of isomorphism, and Gay- 

 Lussac's law of atomic equality, Berzelius was able to 

 demonstrate Dalton's conception to be applicable to a large 

 range of chemical phenomena. Dulong, in collaboration 

 with Berzelius, determined the exact composition of water 

 (already discovered, but now forcibly corroborated), of 

 carbonic acid, and other bodies. 



1786 1889. Chevreul made a deep study of FATTY 

 SUBSTANCES of animal origin (which led to the making of 

 stearic candles) hence his name of father of the fatty 

 acids; formulated the LAW OF CONTRAST OF COLOURS; 

 published numerous papers ON COLOURS, and the theories 

 expounded therein found a ready application in the colouring 

 of silk, so that several industries are under great obligations 

 to his century of labours. 



1794 1863. Mitscherlich discovered the great physico- 

 chemical LAW OF ISOMORPHISM (1818), " Compounds t/ie atoms 



