178 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[August 27, 1870. 
chemists, it is a kind of alcohol, and its appearance during 
fermentation together with ordinary alcohol is no doubt 
due to a process of the normal kind. 
Another product which I might compare to the car¬ 
bonic acid which I just now showed you, is this beau¬ 
tiful crystalline acid substance, which has been long 
known by the name of succinic acid. It got that name 
from the fact that it was originally prepared from amber. 
By subjecting the amber to dry distillation, succinic 
acid, among other products, is formed. Glycerine and 
succinic acid, as well as common alcohol and carbonic 
acid, are always formed when any kind of sugar is made 
to decompose by the process which is termed alcoholic 
fermentation ; and it is seldom that there are not other 
—and probably, in smaller quantities, several other— 
products formed besides those four. In fact, the dif¬ 
ferent kinds of spirit which are obtained by the process 
of fermentation and subsequent distillation,—I mean 
those kinds of spirit to which no artificial flavouring 
material is added (gin is a general name given to cer¬ 
tain spirits which are flavoured by artificial means), 
such as brandy, rum, and others,—owe their distinctive 
peculiarities to the presence of small quantities of vo¬ 
latile substances which are formed during the process 
of fermentation, regarding which a good deal has been 
observed, and several important facts have been col¬ 
lected. 
There is another process of fermentation which I must 
mention, for it is important from its frequent occurrence, 
and that is a process by which another kind of sugar 
usually, but sometimes common sugar, is transformed. 
The substance which most naturally undergoes this 
fermentation is milk-sugar. These hard lumps in this 
bottle, which if you were to take out and taste, you 
would not imagine to be sugar, are made by the crystal¬ 
lization of the solid substance in whey. The whey is 
evaporated carefully to a small bulk, and this substance 
which results is known by the name of milk-sugar. 
When a solution of this is mixed with cheese, which is 
the best ferment for the purpose, it gradually turns acid. 
I dare say it is known to all of you that milk itself, 
which contains this body, and cheese, or rather caseine, 
dissolved with it, together with the fatty globules of 
milk, when exposed to the air, turns acid. That acidity 
is due to a change which takes place in the sugar. 
The sugar disappears gradually, and is transformed 
into an acid substance of which I have a little bottle 
here. It is a strong acid, and here in anofher bottle are 
a few of its salts,—a lime salt and a zinc salt, which is a 
very beautiful and characteristic compound. I shall 
have occasion hereafter to show you a large bottle which 
is now at work, in which I dissolved, not this particular 
kind of sugar, but the ordinary sugar. I put with it a 
quantity of calcic carbonate, and some old, lean cheese, 
with a considerable quantity of water. The mixture 
was kept at a temperature above blood heat for some 
eonsiderable time, and a compound of lactic acid is being 
formed. That is a process analogous in its general 
features to the fermentation which forms alcohol, but it 
is a change of sugar in which no alcohol is formed. 
Sometimes there is a trace of alcohol, but there is not 
necessarily any, and no carbonic acid is formed; but 
instead of these products, the elements of the sugar 
break up into different groups, and arrange themselves 
in another manner. That is really the nature of the 
process, as far as our most careful experiments have gone, 
and the acid which we make in that way, which is lactic 
acid, or acid of milk, is really sugar, of which the ele¬ 
ments are arranged in a different way, so as to acquire 
acid properties. 
The third process, which I must mention from its 
remarkable products, is one which, perhaps, in some 
respects ought rather to be compared with putrefaction, 
for it is a process which has many of the most important 
characteristics of putrefaction. In order to deal with 
the question of fermentation generally, it is necessary 
to allude to some varieties of such chemical changes 
which are usually classed under the term putrefaction. 
As a general rule, I think the characteristic of processes 
of putrefaction is mainly the unpleasant nature of the 
products which are formed. It is not long since a dis¬ 
tinguished chemist, in speaking of alcoholic fermenta¬ 
tion, said that it is really a putrefactive process; and in 
its intimate nature it is, as far as we know, a process 
much like the truly putrefactive processes, and different 
from the processes of eremocausis or oxidation. This 
other process to which I allude consists in forming the 
acid substance which I have here, and which I will 
not open, because it is not a very pleasant body. It is 
a substance which is known, although I believe not very 
commonly, in butter. The peculiar rancid odour which 
butter acquires when it is kept too long, especially in 
warm weather, is due to a transformation of some of its 
materials into this particular acid, which Chevreul, a 
very distinguished French chemist, separated from but¬ 
ter, and he named it from that circumstance butyric 
acid. If we leave some of this product of the last fer¬ 
mentation—some of this lactate of lime, the lime salt 
of lactic acid—under the same conditions in which it 
was formed, that is, if we leave it in the same vessel in 
which it had been formed from the milk or sugar, and 
leave cheese with it, and keep the mixture warm, the 
lactate will gradually decompose, and carbonic acid will 
be given off together with hydrogen gas, and at the 
same time we find that the lactic acid will be decomposed, 
and in place of it we get this butyric acid, and generally 
some valerianic acid and a little acetic acid. 
Amongst the processes which really are analogous to 
fermentation in their nature, but which differ in one 
particular, I must mention one other, the process of 
forming vinegar, or acetic acid. This large bottle con¬ 
tains vinegar in a form which most of you, I dare say, 
have not seen. These fine white crystals are the pure 
substance which, mixed with water in an impure state, 
are generally known by the trivial name of vinegar. 
We call that acetic acid, or hydric acetate. The for¬ 
mation of this body from alcohol represents a variety 
of fermentation which is of considerable importance 
and of frequent occurrence. Everybody who has no¬ 
ticed the process which takes place when animal or 
vegetable matter is left to itself in contact with air, 
especially in moist localities, must have observed that 
there is a gradual disappearance of the organic matter. 
For instance, if you leave a piece of wood in a moist 
place, under certain conditions of very frequent occur¬ 
rence which are favourable to this process, the wood 
gradually gets soft, and becomes transformed into a 
brown substance, and if you leave it long enough—in 
this country, several years generally would be needed 
for this purpose—it gradually disappears. If you were 
to put a piece of that decomposing wood into a closed 
glass vessel, and examine the air above it, you would 
find that the wood was really burning. I am using the 
word combustion in the ordinary chemical sense—I 
mean by that word that the oxygen of the air which 
you have enclosed with the wood is being taken up by 
the wood, and the products of combustion, carbonic acid 
and water, are being formed from the substance of the 
wood. One great class of the processes of fermentation 
is of that kind. They consist not in a mere breaking 
up of the materials already contained in the organic 
substance, but a change of their arrangements, which is 
due, more or less, to the absorption of oxygen, and this 
formation of acetic acid or vinegar is a case of that 
kind. In fact, if we were to leave some ordinary fer¬ 
mented wort in an open vessel, so that the alcohol were 
left there in the mixture in which it had been formed, 
we should find that the alcohol would gradually dis¬ 
appear and give place to an acid substance. The pro¬ 
cess is well known to wine-makers and to brewers, and 
their art consists, amongst other things, in the avoid¬ 
ance of this process of the oxidation of their alcohol. 
