August 27, 1870.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
177 
are concerned, and in which there is every reason to 
believe that vital organisms, or living beings, take an 
active and leading part. I need not say that, for that 
reason, the explanations which we have, even of the 
simplest and best known of the phenomena of fermenta¬ 
tion, are, as yet, mere sketches of the reality. It is, 
however, not the less useful or the less important to 
know them for that reason. 
When we chemists are classifying substances, we adopt 
a principle of classification which I think is almost in¬ 
evitable, but it may be as well that I should mention 
what it is. We put the simple things together, and the 
complex or difficult things together, and then we try to 
put between them, in as regular an order as possible, the 
intermediate links of the chain by which they can be 
connected; and I believe that our best—I might almost 
say our only—explanations consist in thus arranging, in 
a natural order, the facts which we have to consider, 
and then viewing them, and stating what we see, in the 
clearest and least ambiguous terms. Now, the term 
“organic,” as applied to a certain class of chemical sub¬ 
stances might be replaced—and I think, for some pur¬ 
poses, ought to be replaced—by the term “ complex.” 
The substances which we are in the habit of including 
under the term organic are peculiarly complex ; in fact, 
they are the most complex with which we have to do. 
The phenomena of fermentation relate mainly to them, 
and consist principally of a process of change,—the 
breaking-up of those organic bodies into rather less 
complex substances than themselves,—a process of par¬ 
tial analysis. Of course, when 1 say that, I give what I 
conceive to be a characteristic idea of the general method, 
and I must not be supposed to assert that all processes 
of fermentation are analytical. 
Amongst the characteristics which, I think, are par¬ 
ticularly useful and interesting, as serving to distinguish 
organic from inorganic, complex from simple substances, 
is their different behaviour under heat. I have found 
it exceedingly interesting and instructive to bear in 
mind the fact that while simple and inorganic com¬ 
pounds, as we generally call them, are sometimes de¬ 
stroyed and resolved into other compounds by the action 
of a high temperature, yet many of them are not. 
Amongst inorganic substances we find some which are 
broken up or changed by exposure to a high tempera¬ 
ture, but there are others which can stand even the 
highest temperature without undergoing any permanent 
change, that is to say, they return, on cooling, to the 
same state in which they were before the heat was 
applied. With organic substances that is not the case. 
All organic bodies are broken up into minute particles, 
and assume new arrangements, when they are heated to 
a sufficiently high temperature; and that is, I think, a 
distinction which is of considerable theoretical as well 
as perhaps of some practical importance. 
The processes of breaking up which are effected by 
heat upon organic bodies are, in the very great majority 
of cases, different from those which are effected by the 
action of these wonderful little organisms, the ferments ; 
and it is a peculiarity of the action of the ferments that 
they effect the breaking up—the analysis—of complex 
organic substances, and form products which, for the 
most part, we have obtained from those materials by no 
other process. 
Amongst the processes of fermentation, there is one 
which, from its pre-eminent importance, and from the 
fact that we have had occasion to study it more fully 
than any other, ought to be first mentioned. I allude 
to the process of fermentation by which alcohol is formed 
artificially. I may say, indeed, it is the only process by 
which alcohol is ever made. It is a process which con¬ 
sists in breaking up some kind of sugar, for sugar is a 
word which, although popularly restricted to one par¬ 
ticular substance, which is extracted sometimes from 
the sugar-cane and sometimes from beet-root, is used 
by chemists in a more general sense, serving to cha¬ 
racterize a family of bodies which have much in common 
with one another, being for the most part all of them 
sweet, and containing the same elements, but in slightly 
different proportions. They all possess many proper¬ 
ties which are of some importance. These different 
kinds of sugar are broken up by the action of ferment 
into alcohol, and also into another product, carbonic acid 
gas, which has been long known, and for a long time the 
process of alcoholic fermentation was supposed to consist 
simply in a separation of sugar into these two products, 
alcohol on the one hand and carbonic acid on the other.. 
A more careful examination of the products has shown, 
however, that these two never appear alone. I believe 
I may safely say, from the researches of Pasteur and 
others, that no case of the formation of alcohol by fer¬ 
mentation has been known to occur in which several 
other products have not been formed simultaneously- 
with these two. With regard to the difference of pro¬ 
perties of these two bodies, there are one or two points 
of some little interest, especially this one, that whereas 
alcohol is an eminently combustible substance, and is 
well known to have properties of that kind, being fre¬ 
quently used as fuel, on the other hand, carbonic acid, 
the other chief product, is completely burnt; it is a 
substance incapable of undergoing any chemical change 
whatever analogous to combustion. Alcohol is a sub¬ 
stance which I need not show you, although in its pure- 
state it is not very common ; but I will, in order to re¬ 
mind those of you who may be less familiar w r ith its lead¬ 
ing properties, make a little carbonic acid by a short 
process. I will put a little muriatic acid upon some white- 
marble, and the apparent ebullition which you see takes 
place is known to you all as due to the liberation of car¬ 
bonic acid. You might imagine the thing to be ferment¬ 
ing, only that the process in that case would be less 
rapid. Now, if I plunge this little burning paper gra¬ 
dually into the jar containing the carbonic acid, it 
will burn more and more faintly, and get extinguished 
when it enters the gas ; it is totally impossible to. 
set fire to the gas. And there is one other fact that 
we may notice at the same time—the great specific 
gravity which characterizes this gas. I will show you 
that, in this way. I will go through the motion of 
pouring from this jar containing it into another smaller 
jar, and no doubt the heavy carbonic acid will pass 
from the jar in which I first collected it into the lower 
one, w T here we shall find it by means of the taper as 
before. You see that, on lowering the lighted taper 
into this small jar it is extinguished as it was before. 
I will show you the test by which we usually discover 
the presence of carbonic acid. I have here some water 
containing lime in solution,—some lime-water,—and I 
will pour it into the large beaker glass, in which there 
is probably still some carbonic acid left. You see the- 
solution immediately becomes turbid, or, as we express 
it, a precipitate is formed by the combination of the car¬ 
bonic acid with the lime-water. A compound is formed, 
which is nearly insoluble in the water, called carbonate, 
which goes down as a precipitate. 
In addition to alcohol and carbonic acid, I ought to 
mention another kind of alcohol, which occurs to a con¬ 
siderable extent in some distilleries where raw grain or- 
potato-starch is used. This substance imparts to the 
product a very unpleasant odour, and some unwholesome 
qualities. It is known by the name of fousel oil. It 
does not mix with water, and if I were to pour some of 
it on water it would float, without dissolving to any 
considerable extent. There are some other products- 
which are even more interesting and important; two 
especially I ought to mention. One is the clear sub¬ 
stance which you see in this bottle, and which you might 
imagine to be oil; it is a fluid largely made now, and 
known by the name of glycerine, but in chemical lan¬ 
guage I should say that this was an alcohol. It is a 
substance which, by tasting, you might mistake for sugar, 
for it possesses a sweet taste, resembling sugar, but, to- 
