308 PHYSIOLOGICAL CHEMISTRY. 



moved by coagulation with heat and the nitrate evaporated to a 

 syrup. The crystals which separate after a certain time are recrystal- 

 lized from water after decolorizing with animal charcoal. A pure 

 preparation may be obtained from the commercial milk-sugar by 

 repeated recrystallization. The quantitative estimation of milk- 

 sugar may in part be performed by the polaristrobometer and partly 

 by means of titration with FEHLIN G'S solution. 10 cc. of FEELING'S 

 solution corresponds to 0.067 grm. milk-sugar (in regard to FEH- 

 solution and the titration of sugar, see Chapter XIV). 



RITTHATJSEN has found another carbohydrate in milk which is soluble 

 in water, non-crystallizable, which has a faint reducing action, and which 

 yields on boiling with an acid a body having a greater reducing power. LAND- 

 WEHR considers this as an animal gum. 



The mineral bodies of milk will be treated in connection with 

 its quantitative composition. 



The methods for the quantitative analysis of milk are numerous, 

 and as they all cannot be treated of here, we will give the chief 

 points of a few of the most trustworthy and most frequently- 

 employed methods. 



In determining the solids a carefully- weighed quantity of milk 

 is mixed with an equal weight of heated 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 ashing the milk, using 

 the precautions suggested 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 there- 

 fore, according to SOLDNER, subtract 25$ from the total phosphoric 

 acid found in the milk. The quantity of sulphate in the ash also 

 depends on the burning of the albumins. 



In the determination of the total amount of albuminous bodies 

 we make use of RITTHAUSEN'S method, namely, precipitate the 

 milk with copper sulphate. This method gives incorrect results 

 because the copper hydroxide does not give up all its water of 

 hydration on drying the precipitate, but only after ashing the 

 same. The results for the proteids are therefore somewhat too 

 high. 



The method of PULS and STENBERG consists in first diluting 

 the neutralized milk with some water and then treating with alco- 

 hol until the mixture contains 70-85 vols. per cent alcohol. The 

 precipitate is collected on a filter, washed with warm 70$ alcohol, 

 extracted with ether, dried, weighed, burnt, and the residue re- 

 weighed. The traces of albumin which remain in the filtrate and 



