510 Prof. L. Meyer on the 



so soon as these constants have been definitely determined for 

 each constituent group or element, to calculate the heat of 

 formation of the salt in a manner similar to that by which the 

 molecular w< ight of a compound may be deduced from the 

 atomic weights of its constituents. 



This simple relation could not hold were the heats of for- 

 mation of salts affected hy the affinity of the constituents for 

 each other ; for in such a case each constituent would contri- 

 bute so much the more to the heat of formation the greater 

 the affinity between it and the other constituent with which 

 it combined. We must therefore believe that the evolution of 

 heat, developed by the formation of a compound, residts solely 

 from the change of condition of the constituent elements. Similar 

 laws, as Ostwald has shown, apply also to other changes of 

 condition, e. g. to expansion or contraction, or to change of 

 optical properties which accompany the formation of salts. 

 These also can be calculated by simple addition; for their 

 constituent numbers are constants belonging to each one of the 

 reacting substances, and are independent of the nature of the 

 other. 



The thermal theory of affinity has a changed complexion 

 owing to this discovery. What was formerly attributed to 

 the mutual action of several substances must now be regarded 

 as change of condition of each individual substance, each being 

 wholly independent of all others with which it may combine. 

 The heat- change accompanying a chemical change must no 

 longer be regarded as the conversion of potential energy into 

 kinetic energy, owing to the mutual attraction of the atoms ; 

 but it must be concluded that each substance, each atom, each 

 compound, possesses its own peculiar store of available energy, 

 capable of being increased or diminished by its entering into 

 reaction, or by any change of condition. But this store of 

 energy and its changes must in nowise be confounded with 

 affinity — that is, with the reason of chemical change. For 

 the amount of energy lost by a substance during reaction 

 depends solely on its own nature, and on the kind of change 

 which it undergoes; not on the nature of the substance 

 through whose influence this change is produced. To employ 

 an old simile, affinity acts like the spark to the powder ; like 

 the trigger which releases the weight by w r hich, under the 

 action of gravity, the pile is driven in. Just as in these and 

 similar cases there is no proportionality between the effective 

 cause and the final result, so also with chemical changes. 



Such considerations lead naturally to the old question re- 

 garding the necessity of imagining any special affinity or 

 attracting-power between atoms. And the more proofs are 



