78 CELL-CONTENTS AND CELL-WALLS. 



lather is produced ; (ii) add some sodium chloride the soap is 

 separated and rises to the surface as a curd ; (iii) add calcium 

 chloride a precipitate of calcium soap (calcium stearate, etc.) is 

 produced. 



(c) Neutralise filtrate from a with dilute soda ; evaporate it to a 

 syrup on a water bath. Add alcohol, which precipitates the sodium 

 sulphate, and pour off the liquid (alcoholic solution of glycerine). 

 Evaporate this, and test for glycerine as below. 



(d) Tests for Glycerine. (1) Heat a little glycerine with 

 powdered potassium hydrogen sulphate, and note the pungent smell 

 of acrolein this indicates the presence of glycerine. (2) Add a 

 few drops of copper sulphate solution, then some potash a deep 

 blue colour is produced but no precipitate, since glycerine prevents 

 the precipitation of cupric oxide by alkalis. (3) Add drop by drop 

 a 20 per cent, aqueous solution of glycerine to a 5 per cent, solu- 

 tion of borax, to which enough phenolphthalein has been added to 

 produce a distinct red colour ; the red colour disappears, but on 

 boiling it returns if excess of glycerine has not been used. This 

 reaction is also given by other polyhydric alcohols. 



(e) Grind up a few Castor Oil seeds with about 30 c.c. of water 

 to which a drop of chloroform has been added. Divide the liquid 

 into two exactly equal portions, place them in two test-tubes, and 

 at once boil one to destroy the enzyme (lipase). Then add to each 

 1 c.c. of dilute acetic acid, and place both tubes in a bath at 40 C. 

 for half an hour or an hour. Then add to each tube a few drops of 

 phenolphthalein and titrate with decinormal caustic soda solution. 

 Note that the number of c. c. of soda solution required to neuti alise 

 the tube with unboiled enzyme will be greater than in the tube with 

 boiled enzyme. 



(/) In the hydrolysis of oils in the intestine, emulsification 

 occurs. (1) To some Linseed, Olive, or Castor oil in a test-tube, 

 add a little water ; close the tube with the thumb or a cork, and 

 shake vigorously. On letting the tube stand the milky appearance 

 is lost, the oil and water separating again into two layers this is 

 only temporary emulsification. (2) Repeat the experiment, but 

 this time add a little carbonate of soda to the water before shaking 

 up the emulsion produced this time is of a more permanent 

 character. 



(g) The emulsification produced by alkalis is due to the presence 

 of free fatty acids in most oils. If a perfectly neutral oil is shaken 

 up with alkali, no emulsion is formed. 



To detect free fatty acid in a fatty oil, add a drop of phenol- 

 phthalein to a little alcohol in a test-tube, then a drop or two of very 

 dilute soda just enough to produce a red colour. Then add a 

 little olive oil dissolved in ether, or castor oil dissolved in alcohol. 

 The presence of fatty acid is shown by the disappearance of the 

 red colour. 



