1864. ] Hlementary Chemistry. 565 
possesses a soporific virtue.” In confirmation of this remark we will 
make a few extracts from Dr. Apjohn’s pages. When describing the 
process of filling a balloon with dry hydrogen, he says, “* The oil of 
vitriol and potash, in consequence of their great affinity for moisture, 
dry the gas in its passage to the balloon, and at the same time slightly 
augment its levity.” (p. 135.) That oil of vitriol and potash absorb 
moisture when exposed to the air, and that heat is developed when 
they are mixed with water, are facts. We pass beyond our knowledge 
when we infer from these facts the existence of a cause, resident in 
these bodies, which we call their affinity for water. And when we 
proceed to speak of this supposed force as accounting for the ab- 
sorption of moisture or the development of heat, we are simply 
deluding ourselves with words. 
The same remarks will apply, mutatis mutandis, to other similar 
passages. “Sulphur and iron filings, when mixed and moistened 
with water, have a strong affinity for oxygen. If, therefore, such 
a mixture be placed in a light capsule floating on water, and that a 
bell-shaped or cylindric jar be inverted over it, the oxygen of the air 
is gradually absorbed, and the residual gas is nitrogen.” (p. 170.) 
And again, with reference to the supposed isolation of fluorine by 
the action of chlorine gas on fluoride of silver, Dr. Apjohn says :— 
“ Such an experiment could not be made with any prospect of suc- 
cess in glass or even in a platinum vessel; for though the fluorine 
was set free, such is the energy of its affinities that it would at once 
enter into combination by acting on the materials of which the appa- 
ratus was composed.” (p. 378.) 
It we may put confidence in Kimmerer’s results, “ the energy of 
its affinities ’ does not produce this effect. A single line will furnish 
us with one more example: “ Phosphorus is a very inflammable sub- 
stance, the result of its strong affinity for oxygen.” (p. 388.) 
We will quote, lastly, from Dr. Apjohn’s introduction, his general 
account of the theory of chemical affinity. It is a clear statement 
of the common doctrine on the subject. 
“ We come now to the consideration of affinity, the force in virtue 
of which two or more simple atoms combine so as to form a compound 
atom. It is to the chemist the most important of the forces active in 
nature ; for to it he refers the numberless combinations and decompo- 
sitions of which bodies are susceptible.” 
Now, there is no point, in our opinion, which it is more important 
to set plainly before a student, than the fact that, as to the cause of 
chemical change—the forces, if there be forces, which move the 
atoms, if there be atoms—we know nothing at all. Science has to do 
with motion, with changes, with relations, but not with force. Pro- 
bably, if the term “affinity” could be got rid of altogether, it would be 
a gain to chemistry; but at least it should be used only, as “ vital 
force” is still sometimes used, under protest, as a name for the 
unknown cause or causes of chemical action. 
But it is not only in the philosophy of chemistry that this negli- 
gence in distinguishing between fact and hypothesis is observable. In 
