Affinity and Heat. 297 
and independent definition of special facts, the considera- 
tion of primary causes leads us, oftener than we suppose, 
into really begging the question, 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 archée to which are 
referred all facts which are not understood, and which 
thenceforth 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 
teferred in the lump to an entirely unknown cause. It 
was certainly supposed that they belonged to the same 
category when the name was given to them. But the legi- 
timacy 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 a part 
in the action? These phenomena may, perhaps, be here- 
after explained in an essentially different manner, accord- 
ing 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 sul- 
phuric 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 attention ought to be fixed on the observation and 
numerical determination of these effects, which alone are 
within our reach. By this work their differences and ana- 
logies are established, and new light results from these 
comparisons and these measurements. 
Thus, heat and affinity are constantly concerned in our 
chemical theories. Affinity eludes us entirely; yet we 
attribute to it the combination which is the effect of the 
unknown cause. Let us then investigate merely the 
physical circumstances which accompany combination, and 
we shall see how many curious approximations, how many 
measurable phenomena, present themselves 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 vzs viva, we shall at once see how fruitful 
