656 MILK. 



The mineral, bodies of milk will be treated in connection with its quan- 

 titative composition. 



The methods for the quantitative analysis of milk are very numerous, 

 and as all cannot be treated here, we will give the principal points of a 

 few of the methods considered most trustworthy and most frequently 

 employed. 



In determining the solids a carefully weighed quantity of milk is mixed with 

 an equal weight of heated quartz sand, fine glass powder, or asbestos. The 

 evaporation is first done on the water-bath and finished in a current of carbon 

 dioxide or 'hydrogen not above 100 C. 



The mineral bodies are determined by incinerating the milk, using the pre- 

 cautions mentioned in the text-books. The results obtained for the phosphoric 

 acid are incorrect on account of the burning of phosphorized bodies, such as 

 casein and lecithin. We must, therefore, according to SOLDNER, subtract in round 

 numbers 25 per cent from the total phosphoric acid found in the milk. The 

 quantity of sulphate in the ash also depends on the combustion of the proteins. 



In the determination of the total amount of proteins RITTHAUSEN'S method 

 is employed, namely, the precipitation of the milk with copper sulphate according 

 to the modification suggested by MuNK. 1 He precipitates all the proteins by 

 means of cupric hydroxide at boiling heat, and determines the nitrogen in the 

 precipitate by means of KJELDAHL'S method. This modification gives more 

 exact results. 



According to SEBELIEN'S method, three to four grams of milk are diluted 

 with an equal volume of water, a little common-salt solution added, and the 

 proteins precipitated with an excess of tannic acid. The precipitate is washed 

 with cold water, and then the quantity of nitrogen determined by KJELDAHL'S 

 method. The total nitrogen found when multiplied by 6.37 (casein and lactal- 

 bumin contain both 15.7 per cent nitrogen) gives the total quantity of proteins. 

 This method, which is readily performed, gives very good results. I. MUNK 

 used this method in the analysis of woman's milk. In this case the quantity 

 of nitrogen found must be multiplied by 6.34. G. SIMON 2 found that the 

 precipitation with tannic acid, also with phosphotungstic acid, is the simplest 

 and most accurate. The objection to this and other methods in which the pro- 

 teins are precipitated is that perhaps other bodies (extractives) may be carried 

 down at the same time (CAMERER and SOLDNER 3 ) . It is not known to what 

 extent this takes place. 



A part of the nitrogen in the milk exists as extractives, and this nitrogen is 

 calculated as the difference between the total nitrogen and the protein nitrogen. 

 According to MUNK'S analyses about -j^ of the total nitrogen belongs tp'the extract- 

 ives in cow's milk. CAMERER and SOLDNER determine the nitrogen in the filtrate 

 from the tannic-acid precipitate by KJELDAHL'S method, and also according to 

 HUFNER'S method (hypobromite). In this way they found 18 milligrams of 

 nitrogen according to HUFNER (urea, etc.) in 100 grams of cow's milk. 



To determine the casein and albumin separately we may make use of the 

 method first suggested by HOPPE-SEYLER and TOLMATSCHEFF/ 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 pre- 



1 Ritthausen, Journ. f. prakt. Chem. (N. F.), 15; I. Munk, Virchow's Arch., 134. 



2 Sebelien, Zeitschr. f. physiol, Chem., 13; Simon, ibid., 33. 



8 Zeitschr. f. Biologic, 33 and 36. 



4 Hoppe-Seyler, Med. chem. Untersuch., 272. 



