THE ATOMIC VIEW OF NATURE. 



435 



This idea of the rectilinear motion of the particles of 

 matter in a free, i.e., a gaseous, state (the first attempt to 

 explain the physical properties of matter by giving a 

 numerical value to a molecular, not molar, quantity) was 

 not regarded by chemists, for it was indeed of little use in 

 explaining chemical combinations and reactions. It, how- 35. 



. IT- i-i Clausius's 



ever, very soon received an important addition under the firstmemoi 

 treatment of Clausius. 1 



The kinetic theory of gases had not been propounded 

 for the purpose of explaining chemical phenomena; it 

 had grown out of repeated attempts to explain the nature 

 of heat, and the fact, established about ten years earlier 

 by Mayer and Joule, that heat can be transformed into 

 the mechanical energy of molar motion. The idea sug- 

 gested itself that if heat can disappear and be replaced 

 by the measurable motion of molar (measurably large) 

 masses, and vice versd, heat itself may be merely the 

 energy of the directly immeasurable movements of mole- 

 cular (immeasurably small) masses ; and as every body 



made their careful experiments, 

 that if gaseous bodies were allowed 

 to expand, without doing work, 

 no change of temperature took 

 place i.e., that heat neither ap- 

 peared nor disappeared. This would 

 mean that no work of either repel- 

 ling or attracting forces was done. 

 Joule and Thomson showed that 

 there was indeed a very slight cool- 

 ing, indicating that a small amount 

 of heat or energy was used up in 

 doing work against attracting forces 

 the forces of cohesion. Had re- 

 pelling forces existed, their work 

 would have shown itself in a rise of 

 temperature. This line of reason- 

 ing will occupy us in a subsequent 

 chapter (see 0. E. Meyer, ' Theorie 

 der Gase,' vol. i. p. 7, &c., also 



Joule's 'Scientific Papers,' vol. ii. 

 p. 216, &c.) 



1 How little chemical and physical 

 reasoning went hand in hand before 

 the middle of the century is seen 

 from the fact that only after Clau- 

 sius had published his first paper 

 (see note, p. 433), in which he came 

 to the conclusion that the molecules 

 or smallest physical particles of 

 simple (elementary) substances con- 

 sist of several atoms, was his atten- 

 tion drawn to the fact that some 

 French chemists, notably Dumas, 

 Laurent, and Gerhard t, had already, 

 by different arguments, arrived at 

 the conclusion that the molecules 

 of simple (elementary) gases consist 

 of several atoms (see Clausius, loc. 

 cit., p. 22, &c.) 



