624 MILK. 



in which the casein is precipitated by magnesium sulphate. According 

 to SEBELIEN the milk is diluted with its own volume of a saturated 

 magnesium-sulphate solution, then saturated with the salt in substance, 

 and the precipitate then filtered and washed with a saturated magnesium- 

 sulphate solution. The nitrogen is determined in the precipitate by 

 KJELDAHL'S method, and the quantity of casein ( + globulin) determined 

 by multiplying the result by 6.37. The quantity of lactalbumin may be 

 calculated as the difference between the casein and the total proteins 

 found. The lactalbumin may also be precipitated by tannic acid from 

 the filtrate from the casein precipitate containing MgSO 4 , after dilut- 

 ing with water, the nitrogen determined by KJELDAHL'S method and the 

 result multiplied by 6.37. 



SCHLOSSMANN l 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 nitrate 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 weigh- 

 ing 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 numerous other methods 

 for estimating milk-fat, but they cannot be considered here. 



In determining the milk-sugar the proteins are first removed. For 

 this purpose we precipitate either with alcohol, which must be 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 XV). 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 0.0676 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 J-l per cent of sugar. In regard to the 

 modus operandi of the titration we must refer the reader to more com- 

 plete works. 



Instead of these volumetric determinations other methods of estima- 

 tion, such as ALLIHN'S method, the polariscope method, and others,, may 

 be used* In calculating 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 



1 Zeitschr. f. physiol. Chem., 22. 



2 Chemie der menschlichen Nahrungs- und Genussmittel, 4. Aufl. 



