366 M. H. Sainte-Claire Deville on Affinity and Heat. 



tion and contenting ourselves with specious explanations which 

 cannot stand a severe criticism. Affinity especially, defined as 

 the force which determines chemical combinations, has been for 

 some time and still is an occult cause, a sort of archie to which 

 are referred all facts which are not understood, and which thence- 

 forth are considered to be explained, whereas they are only 

 classed, and often badly classed. Thus to the catalytic force* 

 are attributed a host of phenomena which are very obscure, and 

 will remain so, I imagine, if they are referred in the lump to 

 an entirely unknown cause. It was certainly supposed that 

 they belonged to the same category when the same name was 

 given to them. But the legitimacy of this classification even has 

 not been demonstrated. What can be more arbitrary than to 

 class together the catalytic phenomena which depend on the 

 action, or on the presence of spongy platinum or of concentrated 

 sulphuric acid when the platinum and the acid, so to say, take 

 no part in the action ? These phenomena may perhaps be here- 

 after explained in an essentially different manner, according as 

 they have been produced under the influence of an eminently 

 porous substance like spongy platinum, or under the influence of 

 a very energetic chemical agent like sulphuric acid. 



Hence in our investigations we must omit all those un- 

 known forces to which recourse has been had only because their 

 effects have not been measured. On the other hand, all our at- 

 tention ought to be fixed on the observation and numerical de- 

 termination of those effects, which alone are within our reach. 

 By this work their differences and analogies are established, and 

 new light results from these comparisons and these measurements. 



Thus heat and affinity are constantly concerned in our che- 

 mical theories. Affinity eludes us entirely ; yet we attribute to 

 it the combination which is the effect of this unknown cause. 

 Let us then investigate merely the physical circumstances which 

 accompany combination, and we shall see how many curious ap- 

 proximations, how many measurable phenomena, present them- 

 selves to us at 'every moment. Heat, they say, destroys affinity ; 

 let us, then, persistently investigate the decomposition of bodies 

 under the influence of heat estimated in quantity or work, 

 in temperature or vis viva ; we shall at once see how fruitful is 

 this study, and how independent of hypothesis, of any unknown 

 force, unknown even from the point of view of the kind of unit 

 to which its exact or approximate measure is to be referred. It 

 is in this sense especially that affinity, regarded as a force, is an 



* This applies to the forces recently invented — force of diffusion, force 

 of solution, crystallogenic force, and all special attractive and repulsive 

 forces which are brought in to explain the phenomena of calefaction, super- 

 fusion, electrical phenomena, &c. 



