IMPROVED METHODS FOR FAT ANALYSIS. 101 



the marc of fruits, tends to rapidly increase the amount of free acids. 

 Acidity is not a measure of rancidity, as hydrolysis may result from the 

 action of enzymes (lipases) in the presence of moisture without accompa- 

 nying oxidation, which appears necessary for the production of strong- 

 smelhng, acrid-tasting bodies (such as aldehydes, ketones, free volatile 

 acids and esters of acids of low molecular weight) that characterize rancid 

 products. Rancidity is due, apparently, to the simultaneous action of 

 oxygen and of light on free fatty acids, and on glycerol. The latter does 

 not seem to occur free, but appears to be decomposed immediately on 

 formation. Rancidity develops more readily in liquid oils in which olein 

 predominates than in the sohd fats which are composed more largely of 

 palmitin and stearin. Fresh animal fats are practically free from acid, 

 while vegetable oils seem to contain a small amount. Relatively large 

 amounts of free fatty acids are sometimes found in corn, sesame, peanut, 

 rice, olive (especially "bagasse" olive oils), and Japanese sardine oils, in 

 the so-called vegetable butters and tallows and other vegetable fats, par- 

 ticularly palm oil, and in bone fat, beef tallow and butter. The amount 

 .of free fatty acids in waxes is probably smaller and the variation less than 

 in oils and fats, although carnauba wax and especially beeswax appear to 

 contain considerable. In a measure, acid number indicates "quaUtj^" of 

 the product. 



Mineral acids when present may be determined by shaking out vnth 

 hot water in a separatory funnel, and by titrating the solution when cold 

 with N/2 or N/10 allcali (according to the amount of acids present), using 

 1 cubic centimeter of methyl orange (1 to 1,000) as indicator. Methyl 

 orange is not affected by carbonic acid, or by the insoluble fatty acids, 

 and only to a hmited extent by the soluble fatty acids, and is, therefore, 

 well adapted for the purpose. 



Mineral lubricating oils should not contain an appreciable amount of 

 free acids. The acidity may be due to sulfuric acid from the refining 

 process, to resinous bodies or to naphthenic acids. These acids should be 

 neutralized with alkaU and removed by washing or by sedimentation and 

 filtration. 



Ether (Ester) Number, 



The ether number indicates the number of milligrams of potassium 

 hydroxide required for the saponification of the neutral esters in 1 gram 

 of an oil, fat or wax. 



The ether number is represented by the difference between the saponi- 

 fication and acid numbers, and in cases where there are no free fatty 

 acids present is identical with the saponification number. 



Supplementary Notes. — Natural fats, both animal and vegetable, con- 

 tain practically only triglycerides, — neutral glyceryl esters. These glyc- 

 erides may occur, however, to some extent as complex molecules (mixed 

 triglycerides) instead of simple. The composition of mixed glycerides is 

 diflEicult to deternaine, as they appear to suffer intramolecular changes on 

 being treated with a solvent. 



