MILK, FLOUR, AND BREAD. 71 



divide it into two and boil one = a precipitate of serum- 

 albumin. Filter, and keep the nitrate to test for sugar. 

 To the remainder add potassic ferrocyanide, which also 

 precipitates serum-albumin. 



(g.) With the second half of the nitrate test for milk-sugar 

 or lactose with Fehling's solution, or by Trommer's test 

 (Lesson II., 6; IV., b., c.) Instead of proceeding thus, test 

 for the presence of a reducing sugar with the filtrate of (f.) 

 after the separation of the serum-albumin. 



(h.) Scrape off the residue of casein and fat from the filter 

 (f.) ; 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 does not do so. 



2. Separation of the Casein by Salt. To one volume of milk 

 in a test-tube, add two volumes of a saturated solution of common 

 salt, and then excess of powdered salt, (or magnesic sulphate may 

 be used). Shake the tube vigorously for a time, when the casein 

 and fat separate out, rise to the surface, and leave a clear fluid 

 or whey behind. This fluid contains the lactose, salts, and 

 serum-albumin. 



3. Separation of the Casein and Fat by Filtration. Using a 

 Bunsen's pump, filter milk through a porous cell of porcelain. 

 The particulate matters casein and fat 



remain behind, while a clear filtrate containing 

 the other substances in milk passes through. 

 The porous cell is left empty and fitted with 

 a caoutchouc cork with two glass tubes tightly 

 fitted into it. One tube is closed with a clip 

 (Fig. 13), and the other is attached to the 

 pump. Place the porous cell in an outer 

 vessel containing milk. On exhausting the 

 porous cell, a clear watery fluid slowly passes 

 through. Test it for proteids and sugar. 

 Notice the absence of fat and casei'n. j^g 13 _ p rous 



Cell for the Fil- 



4. Souring of Milk. Place a small quantity tration of Milk, 

 of milk in a vessel in a warm place for several 



days, when it turns sour and curdles. It becomes acid test 



