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1 8. Milk Fat. (a) Evaporate the ether filtrate from the casein (Experiment 

 13) and observe the fatty residue. The milk fat was carried down with the 

 precipitate of casein and was removed when the latter was treated with ether. 

 If centrifugated milk was used in the preparation of the caseinogen the amount 

 of fat in the ether filtrate may be very small. To secure a larger yield of fat 

 proceed according to directions gjven under (b) below. 



(b) To 25 c.c. of whole milk in an evaporating dish add a little sand or filter 

 paper and evaporate the fluid to dryness on a water-bath. Grind or break up 

 the residue after cooling and extract with ether in a flask. Filter and remove 

 the ether from the filtrate by evaporation. How can you identify fats in the 

 ethereal residue? 



19. Saponification of Butter. Dissolve a small amount of butter in alcohol 

 made strongly alkaline with potassium hydroxide. Place the alcoholic-potash 

 solution in a casserole, add about 100 c.c. of water and boil for 10-15 minutes or 

 until the odor of alcohol cannot be detected. Place the casserole in a hood and 

 neutralize the solution with sulphuric acid. Note the odor of volatile fatty acids, 

 particularly butyric acid. Under certain conditions the odor of ethyl butyrate 

 may also be detected. 



20. Detection of Preservatives. (a) Formaldehyde. In these 

 tests two controls should be run, one with pure milk and one with 

 milk to which a very small amount of formaldehyde has been added. 



I. Leach's Hydrochloric Acid Test. Mix 10 c.c. of milk and 10 c.c. of con- 

 centrated hydrochloric acid containing about 0.002 gram of ferric chloride in a 

 small procelain evaporating dish or casserole and gradually raise the temperature 

 of the mixture, on a water-bath, nearly to the boiling-point, with occasional 

 stirring. If formaldehyde is present a violet color is produced, while a brown 

 color develops in the absence of formaldehyde. In case of doubt the mixture, 

 after having been heated nearly to the boiling-point for about one minute, 

 should be diluted with 50-75 c.c. of water, and the color of the diluted fluid 

 carefully noted, since the violet color if present will quickly disappear. For- 

 maldehyde may be detected by this test when present hi the proportion i : 250,000. 



II. Gallic Acid Test. Acidify 30 c.c. of milk with 2 c.c. of normal sulphuric 

 acid and distil. Add 0.2-0.3 c - c - of a saturated alcoholic solution of gallic acid 

 to the first 5 c.c. of the distillate, then incline the test-tube and slowly introduce 

 3-5 c.c. of concentrated sulphuric acid, allowing it to run slowly down the side 

 of the tube. A green ring, which finally changes to blue, is formed at the junc- 

 ture of the fluids. This is claimed, by Sherman, to be twice as delicate as either 

 the sulphuric acid or the hydrochloric acid test for formaldehyde. 



(b) Salicylic Acid and Salicylates. Remont's Method. 1 Acidify 20 c.c. of milk 

 with sulphuric acid, shake well to break up the curd, add 25 c.c. of ether, mix thor- 

 oughly, and allow the mixture to stand. By means of a pipette remove 5 c.c. of the 

 ethereal extract, evaporate it to dryness, boil the residue with 10 c.c. of 40 per cent 

 alcohol, and cool the alcoholic solution. Make the volume 10 c.c., filter through 

 a dry paper if necessary to remove fat, and to 5 c.c. of the filtrate, which represents 

 2 c.c. of milk, add 2 c.c. of a 2 per cent solution of ferric chloride. The production 

 of a purple or violet color indicates the presence of salicylic acid. 



1 For other tests see Sherman's Organic Analysis, Second Edition, p. 378. 



