butter 
- MILK. 
epee properties of the constituents of the 
fluid. 
The fatty matter of milk obtained by churn- 
ing cream, and which is known by the name 
of butter, differs from the other forms of animal 
fat in several particulars. It yields about 88.5 
per cent. of fixed acids on being saponified, for 
which purpose it requires no more than four- 
tenths of its weight of caustic potassa ; it there- 
fore unites with alkali very easily. Of these 
acids the margaric and oleic are in large propor- 
tion, the stearic existing as a mere trace. Glyce- 
rine, as is the case with other fats, is a constant 
el of the saponification of butter. The great 
istinguishing peculiarity of this form of fatty 
_ matter consists in the production of three volatile 
acids as results of saponification; these have 
been carefully examined and distinguished by 
Chevreul in his admirable work, “ Sur les 
Corps gras.” He has named them the butyric, 
caproic, and capric acids. The production of 
these acids by the action of alkali has been 
traced by Chevreul to the existence of a new 
form of fat which he detected in butter mixed 
_ with the stearine and elain, and to which he 
gave the name of butyrine: thus butter may 
be regarded as composed of three different 
kinds of fatty matter—stearine, elain,; and 
butyrine—the two former yielding by saponifi- 
_ Cation the margaric, oleic, and stearic acids, 
and the latter the three volatile acids above 
mentioned. The proportions of the three kinds 
of fat vary considerably in different specimens 
of butter. The solubility of butter in alcohol 
is stated by Chevreul to be 3.46 parts in 100 at 
_ a boiling temperature, the specific gravity of 
menstruum being 0.822. The stearine 
obtained from the alcohol by cooling is more 
_ ¢rystalline and of a more brilliant white than 
_ that obtained from common fat, and 1.45 parts 
_ require 100 parts of alcohol of specific gravity 
0.622 for its solution. The elain obtained from 
br possesses no peculiar characteristics. 
_ The butyrine when separated from it, which is 
only to be accomplished with difficulty, pos- 
Sesses the following qualities:—it is an oil 
ely of a yellow colour, but some speci- 
‘mens of butter yield it perfectly white; it con- 
Cretes at 32° Fahrenheit, and possesses the 
smell and taste of butter; it mixes with boiling 
alcohol in all proportions; it is soluble in 
anhydrous alcohol. Potassa and the other 
alkalies are not the only substances capable of 
producing the-volatile acids by acting on buty- 
tine. Alcohol if long digested produces a 
Similar effect, as does strong a ite acid, 
and if butyrine be allowed to putrify these 
_ acids are developed. 
_ The casein or cheesy matter of milk which is 
obtained with some slight admixture of the 
Y matter in the production of cheese from 
the skimmed milk has the following chemical 
operties. It is soluble in water after long 
gestion; but this is most likely owing to 
Some decomposition which occurs in it, and it 
1s certain that casein in its pure, undecomposed, 
and dry state is quite insoluble in water. 
Casein, as it exists dissolved in skim milk, is 
Precipitable by the mineral acids and also by 
359 
the acetic acid. The process which Berzelius 
recommends in order to obtain this substance 
is as follows :—Skim milk is to be mixed with 
a small proportion of dilute sulphuric acid, 
which unites with the casein and precipitates 
it in the form of a white clot. This is to be 
well washed with distilled water on a filter in 
order to separate the whey which it contains. 
After this carbonate of baryta and water are to 
be mixed up with the mass, by which means 
the acid is separated and the casein remains 
dissolved in the water, and may be separated 
from the carbonate and sulphate of baryta by 
filtration. Casein obtained by this process is 
more or less soluble in water, and is precipi- 
tated from its aqueous solution by the acids. 
It rapidly undergoes the putrefactive fer- 
mentation. It is soluble in the alkalies and 
in alcohol both boiling and cold, but far more 
so in the former, from which it rapidly deposits 
on cooling. Casein, when dissolved by the 
assistance of the acids, is precipitated by the 
ferro-cyanide of potassium. It is distinguished 
from albumen, with which it possesses many 
physical and chemical properties in common, 
by being precipitated from solution on the ad- 
dition of acetic acid, and the precipitate so 
formed being with difficulty soluble in an 
excess of the precipitant. It must not be 
imagined, however, that albumen under all 
circumstances cannot be precipitated from so- 
lution by the addition of acetic acid, for when 
dissolved in an alkaline solution, that proxi- 
mate principle is immediately thrown down on 
the addition of the acid. Casein, like albu- 
men, always contains some sulphur as a neces- 
sary element in its composition ; the presence 
of this body may be easily shown by boiling 
casein in a concentrated solution of potassa, 
when the liquor rapidly assumes a brown 
colour, and gives out ammonia, an alkaline 
hydro-sulphuret remaining dissolved, which 
may be proved by the solution becoming of a 
deep black colour on the addition of a salt of 
lead. The aqueous solution of casein is pre- 
cipitated by all the earthy and metallic salts 
which precipitate albumen in the dissolved 
state. Tannin precipitates it even from its 
solution in alcohol, notwithstanding that men- 
struum protects it from the precipitating action 
of the acids. The ultimate analysis of casein 
is, according to Thenard and Gay Lussac, 
carbon 59.781, nitrogen 21.381, hydrogen 
7.429, and oxygen 11.409. Caseous matter, 
as precipitated by rennet in making cheese, is 
liable to a peculiar kind of putrefaction, which 
has been investigated by Proust and Braconnot; 
the latter obtained as a product of putrefaction 
a peculiar crystalline substance, to which he 
gave the name of aposepedine, from ago and 
onwsdwv, indicative of its origin. Proust had 
before noticed this substance and called it 
caseous oxide. It may be prepared very easily 
by allowing cheese to putrify under water and 
evaporating the solution so obtained to dry- 
ness ; the dried mass is then to be treated with 
alcohol until that menstruum exerts no further 
solvent action ; the portion insoluble in alcohol, 
on being dissolved in water, and digested with 
