126 ON TI1E SO-CALLED “ INACTIVE” CONDITION OF SOLIDS. 
Exp. 5.—Dry iron-filings, gently placed in soda-water, liberated an abundance of 
gas, and some of the filings were raised from the bottom to the surface by gas-buoys. 
Exp. 0.— Iron-filings, shaken up with spirits of wine, gently deposited on a fresh 
quantity of soda-water, sank without liberating any gas. 
But, it will be said, that the filings in Exp. 5 were full of air, which was absent in 
the filings used in Exp. G. Now let us see whether air has really the function assigned 
to it of liberating gases from their solutions. 
Among the apparatus of this college is a closed cylinder of fine wire-gauze 
inches long and 2 inches in diameter. Attached to the centre of one end is a wire stem 
7 inches long, which is used for a handle. By means of this piece of apparatus, a 
beautiful experiment on the adhesion of water to a solid is shown. The cylinder can 
be completely filled with water, and carried about without its escaping. It is, however, 
necessary to the success of this result that the wire-cage be chemically clean ; accord¬ 
ingly wc are in the habit of washing it in a weak solution of caustic potash before 
attempting to use it. 
Exp. 7.—The wire-cage was washed in spirits of wine, then plunged several times in 
clean water, and placed, empty but wet, in soda-water. There was no escape of gas. 
The cage was lowered to the bottom of the solution so as to have a mass of air in the 
midst of it; but still no escape of gas, except from that portion of the wire handle that 
had not been dipped into the spirit and was not chemically clean. Soda-water gradu¬ 
ally filtered into the cage, which was taken out three-fourths full of liquid, from which 
there was no escape of gas. It was repeatedly immersed in the solution, and when at 
length it was taken out and shaken, the stream of liquid falling into the liquid in the 
glass produced a slight effervescence. 
I must claim for this experiment the conclusion that the presence of air is not con¬ 
cerned in liberating the gas from its solution. 
Now let us see what is the action of the cage when not chemically clean. 
Exp. 8.—About half a drop of oleic acid was rubbed between the palms of the hands, 
and these were brought into contact with the cage. No sooner did the cage touch the 
soda-water than there was an audible boiling effervescence, which became more abun¬ 
dant on lowering the cage; even the sides and bottom of the glass, which before were 
chemically clean and were quite free from bubbles, became covered with large adhering 
bubbles. 
But the action of heat, it is said, renders solids inactive by removing the gas from 
them by expansion. Of course, according to my view, the action of flame is to burn off 
impurities, and so render the solid chemically clean. If the theory which I am oppos¬ 
ing be true, a body raised in any way to a high temperature will have its surface 
deprived of air, and so will not be in a condition to liberate gas. Let us see. 
Exp. 9.—A glass rod that had long been exposed to the air was put into olive oil, and 
this was raised to the temperature of 310° F. It was left in the oil about twenty 
minutes, then taken out and passed hastily through a duster to get rid of the excess of 
oil. and so plunged into soda-water. It was instantly and completely covered with 
bubbles; so much so, that no part of the immersed portion was free from them. 
Here the rod had not only lost its supposed film of air, but was covered with a thin 
layer of oil; it was, in fact, about as chemically unclean as it well could be, and in this 
state it exhibited the strongest adhesion for air, and little or none for water. 
I cannot help thinking that in examining the phenomena in question, sufficient 
attention has not been bestowed on the remarkable difference between a chemically 
clean and an ordinarily clean surface. A body that is capable of performing certain 
offices at one time becomes incapable of doing so at another, and the circumstances 
which lead to the altered condition are apparently insufficient to produce such marked 
differences. This has thrown an air of mystery over certain phenomena which seem to 
me to admit of very simple explanation. I believe that most, if not all, of the pheno¬ 
mena connected with the crystallization of supersaturated solutions depend on this 
principle of adhesion ; but I propose to refer to this subject on another occasion. I 
must, however, insist on the necessity of distinguishing between the presence or absence 
of the condition of chemical purity of a surface, as the key to the explanation of a large 
class of phenomena. I must further remark that it is difficult to maintain the condition 
of chemical purity for any length of time in apparatus wnth wffiich one is working. A 
slight touch, an open door, a puff of smoke, a draught bringing dust is often sufficient 
to disturb it; as, for example,— 
