602 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



The united ethereal extracts are evaporated nearly to dryness in a current 

 of carbon dioxide ; absolute dryness is avoided as it causes pigmentation of 

 the fatty acids. The residual solution is left to stand in an atmosphere of 

 CO 2 for about 12 hours. A brown crystalline mass remains. 

 This is dissolved in about 50 c.c. of petrol ether boiling at 40- 

 60 and the solution is filtered through asbestos 1 contained in 

 a small glass cup upon a platinum cone attached to a long 

 tube as in Fig. 86. 



The filtrate is collected in a 250 c.c. separating funnel: 

 the flask is rinsed out with petrol ether and the washings col- 

 lected in the same separating funnel. The filter is also washed, 

 especially the lower end. 



To the solution a^re added 50 c.c. of a mixture of equal 

 parts of strong absolute alcoholic potash and water and a few 

 drops' of phenolphthalein. The contents are shaken for 30 

 seconds. The lower layer is run off, when it has separated, 

 into a 250 c.c. graduated cylinder. The petrol ether is washed 

 with 50 c.c. and 25 c.c. of alcoholic potash as above. The 

 united alkaline alcoholic solutions are acidified with 5 c.c. 

 of concentrated hydrochloric acid. The fatty acids, so pre- 

 cipitated, are extracted by shaking twice with 50 c.c. and 

 once with 25 c.c. of petrol ether, which is siphoned into a 

 CO 2 flask. The funnel is rinsed between each extraction with 

 10 c.c. of petrol ether which is added to the main bulk. The 

 united solutions and washings are evaporated in a current of 

 carbon dioxide till the volume is 20 c.c. This solution is 

 filtered as above through asbestos into a clean weighed glass 

 flask (20-35 g m - i n weight) fitted with a ground-in stopper 

 with short entrance and exit tubes. The flask and filter are 



FIG. 86. 

 (From J.. 

 Physiol., 38, 

 C am- 



291 



versf C Press') washed and the wasnin g s collected. The petrol is distilled off 

 ss '^ in a current of carbon dioxide and the fatty acids dried to 

 constant weight in vacuo at 100 (six hours) and weighed. 



They are dissolved in carbon tetrachloride for determination of the 

 iodine values (p. 180). 



1 The asbestos is treated with caustic alkali and aqua regia and washed with water. 

 It is shaken with water for several hours to tease it. It is poured upon the filter, the water 

 washed away with alcohol and ether, and dried. A layer i cm. deep is advantageous and 

 it should be renewed for each estimation. 



