CH. VI.] SOAPS. 161 



177. To about 10 drops of oleic acid add 10 cc. of boiling dis- 

 tilled water, and to the hot mixture add 10 per cent. NaOH drop by 

 drop till the solution is clear. If an excess be added the excess of 

 sodium ions causes a precipitate (see note below) . A clear solution of 

 a soap, sodium oleate, is formed. Divide this into three portions. 

 To A add a few drops of strong HC1 or H 2 SO 4 till the reaction is 

 distinctly acid. Oleic acid separates out and rises to the surface 

 of the tube. 



To B add finely-powdered sodium chloride and shake. The 

 soap is rendered insoluble and rises to the surface. 



To C add some calcium chloride. A precipitate of an insoluble 

 soap, calcium oleate, is produced. 



NOTE. B illustrates the principle of " salting out," which is used in the 

 manufacture of soaps. The excess of sodium ions in the solution, produced 

 by the addition of the sodium chloride, lowers the solubility of the sodium 

 oleate, which is therefore precipitated. 



178. Boil 2 cc. of olive oil with 5 cc. of a 20 per cent, alcoholic 

 solution of sodium hydroxide in a basin over a small flame for five 

 minutes or until the alcohol has all evaporated away. Add about 

 5 cc. of alcohol and heat again to dryness, stirring the whole time. 

 Add about 50 cc. of distilled water and boil till dissolved. Add 

 solid sodium chloride and stir. The soap formed is precipitated. 

 Filter some off, dissolve in boiling water and repeat the experiments 

 A, B, and C, described in the previous exercise. 



Cholesterol. C^H^OH or C 27 H 45 OH is a secondary 

 alcohol, which is very widely distributed in animal tissues. 

 An isomer, known as phytosterol, is found in many veget- 

 able oils. It was first discovered in gall stones, hence its 

 name. A considerable amount is found in nervous tissues 

 and in egg yolk. In blood serum it is present as an ester, 

 as it is in " lanoline," the fatty matter obtained from 

 sheep's wool. It is readily soluble in acetone, chloroform, 

 ether and benzene. It is only slightly soluble in cold, but 

 easily soluble in hot alcohol. It is soluble in the bile salts. 

 It is insoluble in water, weak acids, and alkalies. 



It crystallises from hot alcohol in rhombic plates, 

 which often have a re-entering (notched) angle. From dry 

 ether, chloroform and benzene it crystallises in needles. 



