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MILK ANALYSIS. 657
cipitate by Kjeldahl’s method, and the quantity of casein (+globulin) drtormined
by multiplying the result by 0.37. The quantity of lactalbumin may be calculated
as the difference between the casein and the total proteins found. The lactal-
bumin may also be precipitated by tannic acid from the filtrate from the casein
precipitate containing MgS04 , after diluting with water, the nitrogen determined
by Kjeldahl’s method and the result multiplied by 0.37.
Schlossmann • suggests an alum solution, which precipitates the casein,
in order to separate the casein from the other proteins, and the albumin is then
precipitated from the filtrate by tannic acid. The nitrogen in the precipitate
is determined by the Kjeldahl method. This method has recently been tested
by Simon and he recommends it highly.
The fat is gravimetrically determined by thoroughly extracting the dried
milk with ether, evaporating the ether from the extract, and weighing the residue.
The fat may be determined by aerometric means by adding alkali to the milk,
shaking with ether, and determining the specific gravity of the fat solution by means
of Soxhlet’s apparatus. In determining the amount of fat in a large number of
samples the lactocrit of De Laval may be used with success. There are numer-
ous other methods for estimating milk-fat, but they cannot be considered here.
In determining the milk-sugar the proteins are first removed. For this pur-
pose we precipitate either with alcohol, which must he evaporated from the filtrate,
or by diluting with water, and removing the casein by the addition of a little acid,
and the lactalbumin by coagulation at boiling heat. The sugar is determined by
titration with Fehling’s or Knapp’s solution (see Chapter XIV). The principle
of the titration is the same as for the titration of sugar in the urine; 10 cc. of
Fehling’s solution correspond to 0.0070 gram of milk-sugar; 10 cc. of Knapp’s
solution correspond to 0.0311-0.0310 gram of milk-sugar, when the saccharine
liquid contains about |-1 per cent of sugar. In regard to the modus operandi
of the titration we must refer the reader to more extensive works.
Instead of these volumetric determinations other methods of estimation, such
as Allihn’s method, the polariscope method, and others, may be used. In calcu-
lating the analysis or in determining the solids it is of importance to remember,
as suggested by Camerer and Soldner, that the milk-sugar in the residue is
anhydrous. Many other methods for determining the milk-sugar have been
suggested and recommended.
The quantitative composition of cow’s milk is naturally very variable.
The average obtained by Konig 2
is as follows in 1000 parts:
Water. Solids. Casein. Albumin. Fats. Sugar. Salts.
871.7 128.3 30.2 5.3 36.9 48.8 7.1
35.5
The quantity of mineral bodies in 1000 parts of cow’s milk is, accord-
ing to the analyses of Soldner, as follows: K2O 1.72, Na20 0.51, CaO
1.98, MgO 0.20, P2O5 1.82 (after correction for the pseudonuclein)
,
C1J1.98 grams. Bunge found 0.0035 gram Fe2 3 , and Edelstein and
Csonka 3
found 0.0007-0.001 gm. Fe20?. According to Soldner the
K, Na, and CI are found in the same quantities in whole milk as in milk-
serum. Of the total phosphoric acid 36-56 per cent, and of the lime
1
Zeitschr. f. physiol. Chem., 22.
2
Chemie der menschlichen Nahrungs- und Genussmittel, 4. Aufl.
3
Bunge, Zeitschr. f. Biol. 10; Edelstein and Csonka, Bioch. Zeitschr., 38.
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