XXII] DAIRY PRODUCTS 297 



57 COLORING MATTERS.-TENTATIVE. 

 Proceed as directed under XI. 



FAT. 



58 PREPARATION OF SAMPLE.— TENTATIVE. 



(a) Alkaline extraction. — Treat about 300 grams of the cheese, cut into frag- 

 ments the size of a pea, with 700 cc. of 5% potassium hydroxid solution at 20°C. in 

 a large, wide-necked flask, shaking vigorously to dissolve the casein. In 5-10 

 minutes the casein will be dissolved and the fat will rise to the surface in lumps. 

 Collect the lumps of fat into as large a mass as possible by shaking gently. Pour 

 cold water into the flask until the fat is driven up into the neck and remove it by 

 suitable means. Wash the fat thus obtained with just sufficient water to remove 

 the residue of the alkali which it may contain. The fat is not perceptibly attacked 

 by the alkali in this treatment, is practically all separated in a short time and is then 

 easily prepared for chemical analysis by filtering and drying as directed in 45. 



(b) Acid extraction. — Pass the cheese through a grinding machine, transfer to a 

 large flask and cover with warm water, using 1 cc. for every gram of cheese. Shake 

 thoroughly and add sulphuric acid (sp. gr. 1.82-1.825) slowly and in small quanti- 

 ties, shaking after each addition of acid. The total amount of acid used should 

 be the same as the amount of water employed. Remove the fat, which separates 

 after standing a few minutes, by means of a separatory funnel, wash free from acid, 

 filter and dry as directed in 45. 



59 EXAMINATION.— TENTATIVE, 

 Proceed as directed under XXIII. 



Estimation. 



60 Gravimetric Method. — Official. 



Cover the perforations in the bottom of an extraction tube with dry asbestos 

 felt, and place on this a mixture containing equal parts of anhydrous copper sul- 

 phate and pure, dry sand to a depth of about 5 cm., packing loosely. Cover the 

 upper surface of this material with a layer of asbestos. Place on this 2-n5 grams of 

 the sample and extract with anhydrous ether for 5 hours in a continuous extrac- 

 tion apparatus. Remove the cheese and grind it with pure sand in a mortar to a 

 fine powder, return the mixed cheese and sand to the extraction tube, wash the mor- 

 tar with ether, add the washings to the tube and continue the extraction for at least 

 10 hours. 



61 Schmidt-Bondzynski Method, Modified. — Tentative. 



Rub up, by means of a glass rod, 1 gram of the homogeneous sample with 9 cc. of 

 water and 1 cc. of concentrated ammonium hydroxid in a narrow 100-125 cc. beaker. 

 Digest the mixture at a low heat until the casein is well softened; neutralize with 

 concentrated hydrochloric acid, using litmus as an indicator and add 10 cc. more 

 of concentrated hydrochloric acid. Add a pinch of sand to prevent bmnping and 

 boil gently for 5 minutes, keeping the beaker covered with a watch glass. Cool 

 the solution, transfer to .a Rohrig tube or some similar apparatus, rinse the beaker 

 with 25 cc. of washed ethyl ether and shake well. Add 25 cc. of redistilled petro- 

 leum ether (b. p. below 65°C.), let the solutions separate and proceed from this 

 point as directed in 12. 



