XIII.] MILK, FLOUR, AND BREAD. 95 



granular-looking precipitate of caseinogen, which, as it falls, 

 entangles the greater part of the fat in it. Precipitation is hastened 

 by heating to 70 C. 



(/.) Filter (e.) through a moist plaited filter. Keep the residue 

 on the filter. The filtrate is clear. Divide it into two portions. 

 Take one portion, divide it into two, and boil one = a pre- 

 cipitate of lactalbumin (serum-albumin). Filter, and keep the 

 filtrate to test for sugar. To the remainder add potassic ferro- 

 cyanide. which also precipitates serum-albumin. 



(//.) Test the second half of the filtrate for milk-sugar. Instead 

 of proceeding thus, test for the presence of a reducing sugar with 

 the filtrate of (/.) after the separation of the serum-albumin. 



(h. ) Scrape off the residue of casein and fat from the filter (/. ) ; wash it with 

 water from a wash-bottle, and exhaust the residue with a mixture of ether 

 and alcohol. On placing some of the ethereal solution on a slide, and allowing 

 it to evaporate, a greasy stain of fat is obtained. 



(i.) To fresh milk add a drop of tincture of guaiacum, which strikes a blue 

 colour ; boiled milk is said not to do so. 



Separation of the Chief Constituents of Milk (Salkowski). 

 Milk diluted with water, precipitated with acetic acid and filtered. 



I ! 



Filter-residue (A) (Caseinogen Filtrate (B). (lact-albumin, milk- 



+ Fat). Extract with sugar, salts), concentrated by 



Ether. evaporation. 



i L_ 



I III 



Residue : Solution Coagulated Further evaporated 



Caseinogen, still evaporated Albumin (E). Calcic phoupJmte (F), 



with fat (C). Butter fat (D). Milk sugar (G). 



2. Separation of Caseinogen by Salts. Saturate milk with 

 magnesium sulphate or sodium chloride. 



The caseinogen and fat separate out, rise to the surface, and leave 

 a clear fluid beneath. Caseinogen, like globulins, is precipitated by 

 saturation with NaCl, or MgSO 4 , but it is not coagulated by heat. 

 It was at one time supposed to be an alkali-albumin, but the latter is 

 not coagulated by rennet. It appears to be a nucleo-albumin (?), 

 i.p., a compound of a proteid with nuclein, the latter a body rich in 

 phosphorus. 



Precipitation of Caseinogen by MgS0 4 . 



I I 



Filter residue Filtrate : Milk, sugar, 



Fat + Caseinogen. albumin, salts. 



Collect the precipitate of caseinogen and fat on a filter and wash it with a 



