QUALITATIVE TESTS FOR FATS 169 



pleasant and persistent, but may be removed by warming the fat in 

 shallow layers, or better by passing a current of dry C0 2 through 

 the liquid fat in a cylinder. After several hours it should be prac- 

 tically free from the odor of petroleum. Small quantities of water 

 in the extracted fat may be removed by filtering through a dry 

 folded filter paper in a jacketed funnel at high temperature. 



237. Qualitative Tests for Fats. On the fat obtained try the 

 following tests : 



1 . Note its appearance. Olein is fluid at ordinary temperature ; 

 palmitin and stearin are solid. Palmitin crystallizes from ethereal 

 solutions in rosettes of fine needles. Stearin separates from alco- 

 holic solutions on cooling in rectangular or rhombical plates. 

 Olein solidifies at about — 50° C. in needle-like crystals. 



2. The acrolein test. Decompose a little of the fat by heat in 

 a crucible or other suitable vessel with some potassium bisulphate. 

 Notice the peculiar irritating vapors arising from the decomposi- 

 tion of the glycerine. 



3. Shake a little of the melted fat with soap "solution" in a 

 test-tube. An emulsion is formed by the fat separating into 

 minute globules which remain discrete. 



4. Determine the melting point. Fill a thin glass spindle with 

 the melted fat, seal the ends and solidify by cooling Attach the 

 spindle to the bulb of a thermometer and place both in a test- 

 tube half full of water. Clamp the test-tube in a beaker of water 

 suspended in a second beaker of water and heat gradually. Note 

 the temperature at which the fat becomes translucent. 



The solidifying temperature of palmitin is about 45° C, and 

 its melting point 50-66 C. Stearin melts at a little higher tem- 

 perature than palmitin, 5 5-7 1 u C. 



5 . Place some of the fat in a casserole with several times its 

 volume of dilute caustic potash solution. Boil for about half an 

 hour. The fat by this time should be saponified. It will now 

 lather with water. 



6. Dissolve a little of the soap from the last experiment in a test- 

 tube with alcohol. Add dilute hydrochloric acid and warm until the 



