MOLECULES' AND ATOMS 809 



not destroyed, or is only altered to a slight extent ; hence, notwith- 

 standing the contraction (compression) involved in its formation, 

 nitrous oxide supports combustion. 



The preceding laws were deduced froni purely experimental and 

 empirical data and as such evoke further consequences, as the law of 

 multiple proportions gave rise to the atomic theory and the law of 

 equivalents (Chapter IV.) In view of the atomic conception of the 

 constitution of substances, the question naturally arises as to what, 

 then, are the relative volumes proper to those physically indivisible 

 molecules which chemically react on each other and consist of the 

 atoms of elements. The simplest possible hypothesis in this respect 

 would be that the volumes of the molecules of substances are equa.1 ; or, 

 what is the same thing, to suppose that equal volumes of vapours and 

 gases contain an equal number of molecules. This proposition was 

 first enunciated by the Italian savant Avogadro in> 1810. It was 

 also admitted by the French physico- mathematician Ampere (1815) 

 for the sake of simplifying .all kinds of physico-mathematical concep- 

 tions respecting gases. But Avogadro and Ampere's propositions were 

 not generally received in science until Gerhardt in the forties had 

 applied them to the generalisation of chemical reactions, and had 

 demonstrated, by aid of a series of phenomena, that' the reactions of 

 substances actually take place with the greatest simplicity, and more 

 especially that such reactions take place between those quantities of 

 substances which occupy equal volumes, and until he had stated the 

 hypothesis in an exact manner and deduced the consequences that 

 necessarily follow from it. Following Gerhardt, Clausius, in the fifties, 

 placed this hypothesis of the equality of the number of molecules in 

 equal volumes of gases and vapours on the basis of the kinetic theory 

 of gases. At the present day the hypothesis of Avogadro and Gerhardt 

 lies at the basis of contemporary physical, mechanical, and chemical 

 conceptions \ the consequences arising from it have often been subject 

 to doubt, but in the end have been verified by the most diverse methods ; 

 and now, when all efforts to 'refute those consequences have proved 

 fruitless, the hypothesis must be considered as verified, 6 and the law of 

 Avogadro-Gerhardt must be spoken of as fundamental, and as of great 

 importance for the comprehension of the phenomena of nature; The 



6 It must not be forgotten that Newton's law of gravity was first a hypothesis, but it 

 became a trustworthy, perfect theory, and acquired the qualities of a fundamental law 

 owing to the concord between its deductions and actual facts. All laws, all theories, ol 

 natural phenomena, are at first hypotheses. Some are rapidly established by their conse-> 

 quencea exactly agreeing with facts; others only take root by slow degreess and there 

 are many which are destined ia be. refuted owing to their consequences being found t^ 

 be at variance with facts. 



