VII] FATS AND ALLIED SUBSTANCES 93 



The properties of soaps in solution are important. When a soap goes 

 into solution, hydrolysis takes place to a certain extent with the for- 

 mation of free fatty acid and free alkali. The free fatty acid then forms 

 an acid salt with the unhydrolyzed soap. This acid salt gives rise to an 

 opalescent solution and lowers the surface tension of the water with the 

 result that a lather is readily formed. 



The property of soaps of lowering surface tension is the reason for 

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

 chapter on colloids, p. 12). 



Expt. 92. 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 divstil off the ether as in 

 Expt. 90. 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 

 dryness 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 Uttle 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 suflBcient of a 1 7o solution 

 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 reaction 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,: 



C3H803=C2H3-CHO-f-2H20. 



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. 



