EXAMINATION OF ADIPOSE TISSUE. 145 



4. Conduct on heating with a half -saturated sodium car- 

 bonate solution: the fatty acids dissolve, carbon dioxide is 

 evolved, and a sodium soap is formed. Cool the test-tube in 

 water: the solution solidifies to a jelly of so-called soap 

 gejatin. 



5. Pour 100 cc. of water upon 2 g. of fatty acids, heat and 

 dissolve the fatty acids by neutralizing with a solution of 

 sodium hydroxide: soap solution. The following reactions 

 are to be made with small portions of this solution while it 

 is still warm. 



(a) Addition of hydrochloric acid: precipitation of fatty 

 acids. 



(6) Addition of calcium chloride solution: insoluble cal- 

 cium soap is formed and the solution loses the property of 

 foaming when shaken. 



(c) Addition of lead acetate: white precipitate, which 

 becomes viscous and sticky on warming; lead plaster. 



(d) Pour on a few cubic centimeters of the soap solution 

 Borne drops of a vegetable oil or cod-liver oil and shake once 

 or twice: homogeneous milky fluid due to the formation 

 of an emulsion. The soaps possess in a high degree the 

 property of emulsifying fats. Repeat the last experiment, 

 using, however, instead of the soap solution, four drops of 

 sodium carbonate solution; emulsion often takes place in 

 this case also, but only when the fat contains free fatty acids, 

 for then soap is formed from the fatty acids and the sodium 

 carbonate. Absolutely neutral fats containing no free fatty 

 acids are not emulsified when treated with sodium carbonate 

 solution. 



(e) Place some fatty acids in a dry test-tube, and in 

 another tube about the same amount of fat. Place both, 

 tubes in a beaker partly filled with water, heat the beaker on 

 the wire gauze, stirring the water constantly with a glass rod 

 (having a piece of rubber tubing on its end), in order to- 



