124 
tlie power possessed by points of facilitating vaporisation 
and crystallisation. 
(C.) Low chemical affinities of catalytes. When it is con- 
sidered that the molecular forces exerted by a catalyte can 
only be employed when the substances to be acted upon are 
brought into very close contact with it, so close that if these 
substances had strong chemical affinities for one another 
they would combine; and when, further, it is considered 
that if the catalyte united chemically with other material 
it would soon cease to exist as such and would lose its 
catalytic power, it becomes obvious that catalytes must be 
chemically indifferent to the substances they act upon, and 
not only is this the case, but all the most energetic catalytes 
display chemical indifference not only towards those sub- 
stances which they affect, but also towards ordinary chemical 
reagents ; instances of this fact were found in the catalytic 
properties amongst metalloids, of charcoal, glass, and sand ; 
amongst metals, of platinum, and others which are least 
affected by oxygen. The researches of Dr. Charles Henry 
and Mr. J. A. ftansome, and of the Rev. J. Eyre Ashby, 
upon the catalytic powers of metals and their oxides, were 
quoted, and the conclusion was drawn that it is not those 
oxides which have an excess of oxygen, nor yet those which 
most readily part with it, but it is the sesquioxides whose 
influence is most felt. It was also pointed out that ferments, 
the most remarkable substances in the organic kingdom for 
their catalytic power, belong universally to the class of 
colloid bodies, one of whose chief characteristics is that of 
“ chemical indifference.” 
(D) The molecules of the catalyte must be free from any 
stain of vapour or any other substance which might partially 
impede its molecular action. The condensation of vapour 
upon solids had been noticed by Professor Magnus and 
Messrs. J anion and Bertrand, and the importance of cleansing 
catalytes by heat or other means was pointed out ; also the 
