172 THE CHEMISTRY OF SOME FOODS. [cH. VII. 



203. The estimation of lactose in milk by the method of 

 Folin and Denis.* 



Principle. Proteins do not interfere with the method of 

 estimation of sugar devised by Folin and McEllroy (Ex. 161). 



Method. Dilute the milk i : 4 (25 cc. to 100 cc.) for cow's 

 milk and i : 5 (5 cc. to 25 cc.) for mother's milk. Fill the special 

 burette with the diluted milk (or use a burette of the usual 

 pattern). 



Into a large tube place 5 grams, of the phosphate powder, 5 cc. 

 of the 6 per cent, copper sulphate, shake and boil. Run in about 

 3-4 cc. of the diluted milk and boil gently for 4 minutes. Complete 

 the titration as described in Ex. 161. 



~ 7 7 .. 4-04 x dilution 



Calculation. - = anhydrous lactose per cent, 



volume required 



NOTE. The average amount of lactose in cow's milk is 4-5 per cent. So 

 about 3-6 cc. of a i in 4 dilution of normal cow's milk is required. 



Inorganic constituents. 



204. Treat the remainder of nitrate C with two or three drops 

 of strong ammonia and boil. A slight gelatinous precipitate of 

 calcium phosphate is produced. Filter through a small paper. 

 Boil 4 cc. of water, to which has been added i cc. of strong acetic 

 acid. Pour the hot solution on to the filter paper, and collect the 

 filtrate in a clean tube. To the filtrate add a solution of potassium 

 oxalate. A white precipitate of calcium oxalate is formed. Treat 

 with i cc. of nitric acid. The precipitate dissolves. Add a few 

 cc. of ammonium molybdate solution and boil. A yellow crystalline 

 precipitate is slowly formed, indicating the presence of phosphates 

 in milk. 



C. Cheese. 



205. Shake some grated cheese in a dry test-tube with ether, 

 and examine the ethereal solution for fat as in Ex. 195. Fats and 

 fatty acids are present in considerable quantity. 



* Journal of Biological Chemistry, xxxiii., p. 521 (1918). 



