vi] THE FATS AND LIPASES 83 



their producing very stable emulsions when added to oil and water (see 

 chapter on colloids, p. 11). 



Expt. 84. Hydrolysis of fat with alkali. Take 12 Brazil nuts, the seeds of Berthol- 

 letia (Lecythidaceae). Crack the seed coats and pound the kernels in a mortar. Put 

 the pounded nut in a flask, cover it with ether, and allow the mixture to stand for 

 2-12 hrs. Filter into a weighed or counterpoised flask and distil off the ether as in 

 Expt. 82. Weigh the oil roughly and add 4-5 times its weight of alcoholic caustic 

 soda (prepared by dissolving caustic soda in about twice its weight of water and 

 mixing the solution with twice its volume of alcohol). Heat on a water-bath until 

 no oil can be detected when a drop of the mixture is let fall into a beaker of water. 

 Then add saturated sodium chloride solution. The soaps will rise to the surface. 

 Allow the soaps to separate out for a time and then filter. Press the soap dry with 

 filter-paper, and test a portion to see that it will make a lather. Neutralize the 

 filtrate from the soap with hydrochloric acid and evaporate as nearly as possible to 

 dry ness on a water- bath. Extract the residue with alcohol and filter. Test the 

 filtrate for glycerol by means of the following tests : 



(a) To a little of the solution add a few drops of copper sulphate solution and 

 then some sodium hydroxide. A blue solution is obtained owing to the fact that 

 glycerol prevents the precipitation of cupric hydroxide. 



(6) Treat about 5 c.c. of a 0'5 / solution of borax with sufficient of a 1 / solu- 

 tion of phenolphthalein to produce a well-marked red colour. Add some of the 

 glycerol solution (which has first been made neutral by adding acid) drop by drop 

 until the red colour just disappears. Boil the solution : the colour returns. The re- 

 action is probably explained thus. Sodium borate is slightly hydrolyzed in solution 

 and boric acid, being a weak acid, is only feebly ionized, and therefore the solution 

 is alkaline. On adding glycerol, glyceroboric acid (which is a strong acid) is formed 

 and so the reaction changes to acid. On heating, the glyceroboric acid is hydrolyzed 

 to glycerol and boric acid, and the solution again becomes alkaline. 



(c) Heat a drop or two with solid potassium hydrogen sulphate in a dry test-tube ; 

 the pungent odour of acrolein (acrylic aldehyde) should be noted : 



C 3 H 8 O 3 = C 2 H 3 CHO + 2H 2 O. 



In addition to Brazil nuts, the following material can also be used : 

 endosperm of Coconut, ground linseed, almond kernels and shelled seeds 

 of the Castor-oil plant (Ricinus): about 50 gms. should be taken in 

 each case. 



Expt. 85. Reactions of soaps, (a) Take some of the soap which has been filtered 

 oft' and shake up with water in a test-tube. A lather should be formed. (6) Make 

 a solution of a little of the soap in a test-tube and divide it into three parts. To each 

 add respectively a little barium chloride, calcium chloride and lead acetate solutions. 

 The insoluble barium, calcium and lead salts will be precipitated. (The curd which 

 is formed in the case of soap and hard water is the insoluble calcium salt.) Thirdly, 

 take the remainder of the soap and acidify it with dilute acid in an evaporating dish, 

 and warm a little on a water-bath. The soap is decomposed and the fatty acids are 

 set free and rise to the surface. 



62 



