EXAMINATION OF FATS. 1429 



ucts, which have a reducing action on silver nitrate. Hence the oils a 

 or fats should be purified before testing. 



To purify the oils and fats, heat from 20 to 30 grams on water bath 

 for a few minutes with 25 cc of 95 per cent alcohol, b shake thor- 

 oughly, decant as much of the alcohol as possible, and wash with 2 per 

 cent nitric acid, c and finally with water. The oil or lard thus purified 

 will give no reduction at all if it contains no cotton-seed oil. Heating 

 the oils or fats to 100 or simple washing with 2 per cent nitric acid is 

 not sufficient, except in a few cases. 



With oils the use of the Halphen and Bechi tests will be found to be 

 useful as a means of approximately determining the amounts of adul- 

 teration present. If Halphen gives a reaction and Bechi does not, 

 the adulteration with cotton-seed oil is probably less than 20 per cent. 



SEPARATION OF ARACHIDIC ACID. 



Saponify 10 grams of oil with alcoholic potash 6 in flask connected 

 with reflux condenser; then add dilute solution of acetic acid to very 

 slight excess. Add enough 95 per cent alcohol to dissolve the free 

 fatty acids, if any separate; then add excess of a saturated solution of 

 lead acetate in 50 per cent alcohol, filter off precipitate of lead soap, 

 wash the soap into a flask by means of a stream of ether, add 100 cc 

 of ether to flask, cork and agitate, and allow to stand for some hours; 

 then filter and wash with ether. The lead soap can be easily washed 

 from the filter paper into a flask b}^ means of a stream of hot water. 



Add an excess of dilute hydrochloric acid, fill up the flask with hot 

 water, allow the free fatty acids to harden and separate from the pre- 

 cipitated lead chlorid, wash, drain, dry, and dissolve the fatty acids in 

 50 cc of boiling 90 per cent (by volume) alcohol. The crystals of 

 arachidic acid separate out as the liquid cools. Cool to 15 to 20 and 

 allow to stand some time. Filter, wash the precipitate twice with 10 cc 

 90 per cent (by volume) alcohol, and then with alcohol of 70 per cent (by 

 volume). Dissolve off the filter with boiling absolute alcohol or ether; 

 evaporate to dry ness in weighed dish, dry, and weigh; add to this weight 



a The writer found, in testing a large number of salad oils, which, according to the 

 Halphen test, contain no cotton-seed oil, that nearly all gave a brown coloration with 

 Bechi reagent, and In some cases reduced silver. These same oils on being purified 

 gave no reaction. 



b Used by the writer and found to be much more convenient and just as satisfac- 

 tory as dilute alkali. 



c Wesson, Jour. Am. Chem. Soc., 1895, 17, 724. 



d Renard, Or., 1871, 73, 1330; Benedikt and Lewkowitech, Oils, Fats, and Waxes, 

 p. 365. 



e This modification of Renard's method was suggested by Tolman (Bull. 65). 

 The use of alcohol in the saponification and precipitation enables one to more readily 

 extract with ether. 



12249 No. 1302 5 



