ICROCHEMIS TRY. Jl 



3. Fats and Fatty Oils. 



107. Under the names fats and fatty oils are included, ac- 

 cording to their consistencies, the glycerine ethers of various 

 organic acids of high molecular weights, especially those of 

 palmitic acid, C 15 H 31 COOH, stearic acid, C 17 H 36 COOH, and 

 oleic acid, C I7 H 33 COOH. 



But beside these, a whole series of acids still partly but 

 little studied have been isolated from the various oils of 

 vegetable origin (cf. Beilstein I, 427). An exact microchem- 

 ical separation of these compounds is not yet possible. 

 Even those reactions which should show whether doubtful 

 substances belong to the group of fats still leave much to 

 be desired in the matter of exactness, since they nearly all 

 occur in the presence of other substances. 



108. In general, however, the fatty oils show the following- 

 reactions : 



They are insoluble in cold and hot water and slightly 

 soluble in alcohol ; but castor-oil forms an exception in 

 being pretty readily soluble in alcohol. 



They are easily soluble in carbon bisulphide, ether, chloro- 

 form, petroleum ether* phenol, ethereal oils (as, e.g., clove- 

 oil), acetone, and wood-siprit (methyl alcohol). 



According to A. Meyer (II), most fatty oils are insoluble 

 \r\glacial acetic acid, if the quantity of acid is not too great, 

 as, for instance, when the reaction is conducted under a 

 cover-glass. 



An aqueous solution of chloral hydrate acts in the same 

 way as glacial acetic acid, according to A. Meyer (II). 



109. Alcannin, the coloring matter contained in the roots 

 of Alcanna tinctoria, colors the fats deep red. The solution 

 used for this reaction may be prepared by dissolving the 

 commercial alcannin in absolute alcohol, adding the same 

 volume of water, and filtering. In this solution the sections 

 to be tested are left for one or two, or better, six to twenty- 

 four, hours. All oil-drops then appear deeply colored; 

 but, on the other hand, ethereal oils and resins show the 



*[This is the benzinuin of the U. S. Pharmacopoeia.] 



