12 INTRODUCTION 



into an alcoholic solution of potassium hydroxide previously heated on 

 a water-bath nearly to boiling. Mix well, and keep the mixture gently 

 boiling on the bath till saponification is complete. This only takes a 

 short time. Remove a little of the soap solution, and drop it into dis^ 

 tilled water in a test-tube. If unsaponified fat is present, it will rise to 

 the top as drops of oil. In this case boiling should be continued. If 

 all the fat has been saponified, the soap solution will mix with the 

 water and no oil-drops will separate. 



4. Fatty Acids. Heat some 20 per cent, sulphuric acid in a small 

 flask nearly to boiling, and drop into it some of the soap obtained in 3. 

 The fatty acids separate put and rise to the top as an oily layer. Cool, 

 skim off the fatty acid, and wash it with distilled water till the wash- 

 water is no longer acid. 



(a) Dissolve a little of the washed fatty acid in ether. Add a few 

 drops of an alkaline solution of phenolphthalein to a few c.c. of water 

 in a test-tube. Drop into this the ethereal solution of fatty acid. The 

 red colour is discharged. 



(6) Put a small portion of the fatty acid on a glass slide resting on a 

 piece of white paper. Place on it a drop or two of a i per cent, solution 

 of osmic acid (osmium tetroxide). The osmic acid is reduced to a lower 

 oxide (which is black) by the action of oleic acid present in the fatty 

 acid mixture, which abstracts some of the oxygen. Any. fat which 

 contains olein or oleic acid, as body-fat does, is therefore blackened by 

 osmic acid. 



(c) Add to a portion of the fatty acid some sodium hydroxide solution, 

 and warm. Sodium soap is formed. Add warm water and shake up. 

 A lather is produced. Keep the soap solution for 6. Keep a little of 

 the fatty acid for 5 (b) and 6 (b). 



5. Glycerin. (a) Add to a little glycerin in a dry test-tube a few 

 crystals of potassium bisulphate (KHSO 4 ), and heat over the free flame. 

 Acrolein is given off, which is recognized by its pungent odour, and by 

 blackening a piece of filter-paper moistened with ammoniacal silver 

 nitrate solution, and held over the mouth of the test-tube. The paper 

 is blackened owing to the reducing action of the vapour on the silver 

 nitrate. 



(b) Repeat this test with lard, and with a portion of the fatty acid 

 from 4. Acrolein will be given off by the lard because glycerin is con- 

 tained in neutral fat, but not by the fatty acid if it has been properly 

 separated from the glycerin. 



6. Emulsification. (a) Take three test-tubes and label them A, B, 

 and C. Put a few c.c. of water in A, a solution of soap in B, and a 

 dilute solution of sodium carbonate or sodium hydroxide in C. To each 

 add a few drops of fresh olive -oil and shake . An emulsion will be formed 

 in B, but not in A. Probably there will be some emulsification in C also, 

 owing to the presence in the oil of some fatty acid, which forms soap 

 with the alkali. But if the oil is free from fatty acid, no emulsion will 

 be formed. 



(b) Repeat (a) with rancid olive-oil, which contains much fatty acid, 

 or with fresh olive-oil to which some of the fatty acid obtained in 4 has 

 been added. A good emulsion will be produced in C as well as in B. 



7. Melting-Point of Fat. Put into a very narrow test-tube or a short 

 piece of narrow glass tubing some finely divided mutton fat, freed, as 

 far as possible, from connective tissue. Fasten the test-tube on to the 

 bulb of a thermometer with a rubber band, and immerse the ther- 

 mometer and tube in a beaker filled with water and standing on a water- 

 bath, which is gradually heated. Observe the temperature at which 

 the fat melts. Repeat the experiment with hog's lard and dog's fat. 



