MINERAL BODIES. 623 



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 they cannot all be treated here, we will give the chief 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 asbestus. 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 

 precautions 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 RITTHATJSEN'S 

 method is employed, namely, the precipitation of the milk with copper 

 sulphate according to the modification suggested by MuNK. 1 He pre- 

 cipitates all the proteins by means of cupric hydoxide 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 lactalbumin 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 phospho- 

 tungstic acid, is the simplest and most accurate. The objection to this and 

 other methods in which the proteins 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 ^ of the total nitrogen belongs to the 

 extractives in cow's milk, and rr in woman's milk. CAMERER and" SOLDNER 

 determine the nitrogen in the filtrate from the tannic-acid precipitate by KJEL- 

 DAHL'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, 4 



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



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



3 Zeitschr. f . Biologie, 33 and 36. 



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



