FATS AND RELATED SUBSTANCES. 63 



An isomeric substance known as isocholesterol is often 

 found associated with the true cholesterol, especially in wool 

 fat. In the vegetable kingdom other forms of cholesterol 

 are widely distributed in small quantities, being found in most 

 oils and seeds. All forms of cholesterol have a marked action 

 on polarized light. 



Ex. If gall-stones are obtainable the following reactions may be carried 

 out in illustration of properties of cholesterol. Crush the stones to a 

 powder and boil with water to remove anything soluble. Extract the 

 residue several times with hot alcohol, filter, unite the solutions and allow 

 the cholesterol to crystallize on cooling. As some fat may be present this 

 must be removed by saponifying with a little alcoholic potassa solution. 

 After saponification boil off the alcohol and extract the dry residue with 

 ether, in which soaps are insoluble. On evaporation of the ether a nearly 

 pure cholesterol is obtained. It may be further purified by recrystalliza- 

 tion from hot alcohol. With the substance these tests may be made: 



SALKOWSKI'S TEST. Dissolve about 10 milligrams of cholesterol in 2 

 cubic centimeters of chloroform and shake with an equal volume of strong 

 sulphuric acid. The chloroform becomes colored blood red, then cherry 

 red and finally purple. The acid shows a dark green fluorescence. If 

 the chloroform is poured into a dish the color changes to blue, then green 

 and finally yellow. 



BuRCHARD-LiEBERMANN TEST. Dissolve about io milligrams of choles- 

 terol in 2 cubic centimeters of chloroform, add 20 drops of acetic anhy- 

 dride and i drop of strong sulphuric acid. A violet pink color results. 



The appearance of cholesterol plates should be studied under the 

 microscope. 



The presence of cholesterol in the ester form in lanolin and 

 similar preparations of wool fat may be shown by the above 

 tests. 



