September 10, is 70.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
215 
fact that it is a cycle, the idea of which implies that the 
road by which it returns is not the same by which it 
goes, and I want that idea to be suggested by the word. 
In the case of etherification, I wish I could lawfully use 
formulae on the black board, but it would not do, for I 
am sure that the greater number of my audience will 
agree with me that it would, be a liberty which I ought 
not to take; but chemists are in the habit of denoting, 
by the aid of formulae, particulars which require to be 
fully explained. I mention that because, excluding that 
ordinary process, the particulars of my argument must, 
of course, be omitted, inasmuch as I do not use the lan¬ 
guage by which alone those particulars can be conveyed. 
When the sulphuric acid acts upon alcohol, and trans¬ 
forms it, by a succession of these cyclical processes, into 
ether and water, the general kind of process is this:—A 
little particle of the acid—because each one acts like the 
rest, and we had better consider one as a sample of the 
rest —first takes something from a contiguous particle of 
alcohol, and then it hands over this something to another 
particle of alcohol. That which the acid takes in the 
first instance is called, in our ordinary language, ethyl. 
It is a group consisting of carbon and hydrogen, very 
much like hydrogen gas—it is a group of those elements, 
and behaves in a manner closely analogous to hydrogen 
itself. The acid, in doing that particular work which 
we have to consider, first takes a particle of this ethyl 
from one particle of alcohol, and whilst it does so, it 
gives to the alcohol something in exchange ; that some¬ 
thing is hydrogen. And by doing this, the sulphuric 
acid which has taken up this ethyl is converted into 
sulpho-vinic acid; it has gone half round the circle, in 
fact. The remainder of its journey consists in reversing, 
in another way, with another particle of alcohol, that 
very same kind of interchange which it had undergone 
in the first instance, that is, it gives up again this little 
portion of ethyl which it had taken, and resumes hydro¬ 
gen in place of it. Just as that is the general process 
when sulphuric acid acts upon alcohol, forming it into 
ether and water, so in the other process, which I just 
now reminded you of, there is a similar action, only there 
is this difference—of course, I speak within those narrow 
limitations which are imposed upon us by our very im¬ 
perfect knowledge of even these best-known processes— 
but, as far as we know, the nitric oxide merely takes up 
oxygen, but gives up nothing in exchange. Those red 
fumes which you saw were really nitric oxide plus oxy¬ 
gen, not nitric oxide in which oxygen had replaced 
something else, and that was a difference between the 
process in that case and in the one to which I just now 
referred. Then, again, it simply gives up that oxygen 
to the particle of sulphurous acid. 
The illustrious Liebig, to whom we owe, in this order 
of phenomena as in every other order which he has 
touched, some of the most valuable ideas which have 
guided our researches, suggested many years ago, for 
the explanation of the phenomena of fermentation, a 
theory which certainly has rendered very great service, 
and not the less so from the fact that it has been replaced 
by one more perfect. In building a house, it is certainly 
no proof that a scaffolding is unnecessary that in the 
final structure the scaffolding is not maintained ; and so 
in the progress of our science, as in every other science, 
each part of the work must be judged from its usefulness 
in aiding the carrying on of the building, even though 
the particular substance which was placed there at the 
time does not finally form part of the structure itself. 
Liebig’s explanation really is classic, and well worthy 
of a few minutes’ consideration. He classed together 
a considerable number of cases of chemical action which 
bore, at least upon their surface, a considerable resem¬ 
blance to one another, and he saw in them something 
in common, and by this one resemblance which they 
had he classed them, considering it to be their essential 
characteristic feature. For example, there is a sub¬ 
stance which is made, by a process of oxidation, of a 
compound something like lime. It is called baric per¬ 
oxide. Thenard had found that the oxygen which is 
here taken up by the baryta can, by a particular pro¬ 
cess, be passed over to water, so that, in fact, Thenard, 
from this oxide of baryta, made, by a process which I 
will repeat on a small scale, some oxidized water, or per¬ 
oxide of hydrogen, as it is commonly called. Here is 
some of the peroxide suspended in water, and by adding 
an acid hydrogen salt, the hydric nitrate, in small quan¬ 
tities (for if I add it in too large quantities, I should 
destroy the peroxide, which is a very tender substance, 
and requires to be treated tenderly), I should gradually 
transfer the oxygen from the baryta, with which it was 
at first combined, to the water which is here present. 
This oxidized water, or peroxide of hydrogen, gives up 
the oxygen which it has just taken up very easily 
indeed; in fact, the difficulty is to prevent it doing so. 
Amongst processes of that kind, I will show you one 
simple one. I will pour into the water in this large 
beaker-glass some of the solution which I have just pre¬ 
pared, and then add to it a few drops of this red liquid, 
which is a solution containing chromic acid combined 
with potash. You see, no doubt, that although I have 
only added half-a-dozen drops, there is evidence of a 
chemical change, and the deep blue colour which is 
formed by the contact of the two liquids is due to the 
formation of a new compound. The chromic acid, which 
has a red colour, takes up oxygen from that peroxide of 
hydrogen, forming a blue compound. I have purposely 
chosen this particular instance, because the process is a 
slow one, and we have time to see its intermediate 
changes. I will leave the glass here, and in a few mi¬ 
nutes you will see the blue colour will have disappeared, 
and in place of it we shall have a dirty green colour, 
hardly visible. Whilst that change takes place, if we 
were to take means to examine carefully what was going 
on, we should find that oxygen gas passed off, and if we 
examined the green substance present at the end of the 
process, and compared it to this original red chromic 
acid, we should find that it consists of chromic acid 
minus oxygen. The peroxide takes away oxygen from 
this chromic acid, and yet the chromic acid has got hold 
of its oxygen pretty firmly; it requires a considerable 
amount of energy to tear away even that part which is 
torn away by the process. But at the same time the 
oxygenated water is losing part of its oxygen. The 
deoxidation of the peroxide induces the chromic acid to 
give up some of its oxygen; the one body induces in the 
other a change similar to that which itself is undergoing. 
The peroxide of hydrogen is losing oxygen, and it makes 
the chromic acid also lose oxygen. To state the process 
in general terms, I may well use the expression of 
Liebig, and call it contagious action. There are many 
other cases of similar processes. Here is a bit of rotten 
wood; if I were to moisten it and put it into a conve¬ 
nient flask, leaving room for a quantity of air, closing 
the mouth of the flask with a good cork, and leaving it 
for a day or two, also putting with the air a little hy¬ 
drogen gas, which, you know probably, is capable of 
combining with oxygen, I should, on examining the 
mixture of air and hydrogen after it had been in contact 
some time with this rotten wood, find that the hydrogen 
had been removed from the air, and at the same time 
the oxygen of the air which had been mixed with it had 
disappeared. Now this wood is actually undergoing a 
process of combustion; it is actually absorbing oxygon, 
or being burnt, very slowly indeed, but still at a rate 
which is not unimportant, if you want it to last for any 
length of time. De Saussure, who noticed this, attri¬ 
buted the oxidization of the hydrogen gas to the fact 
that the wood is itself undergoing oxidation. I will 
take another case of the same kind. I will put into, a 
little flask some of that peroxide of hydrogen, and will 
show you another decomposition of it, which is rather 
more convenient in one respect than the one I first took, 
as it will show us something more of the process. Into 
