IMPROVED METHODS FOR FAT ANALYSIS. 115 



meters of filtrate should give a decided color with three or four drops of 

 N/10 allcali, using phenolphthalein as indicator. In those cases where 

 caprylic and particularly capric acids are present the filtrate may give an 

 appreciable acid reaction after 10 to 15 washings. The treatment should 

 be continued until the acidity of the filtrate is less than 0.25 cubic centi- 

 meter N/10 solution. 



In determining the insoluble acids of oils and fats having a low solidi- 

 fying point, the addition of .5 to 1 gram of ceresine ^ before treating with 

 sulfuric acid greatly facilitates subsequent work, and serves to protect 

 the unsaturated acids from decomposition. 



The filter and inverted flask containing the cake of insoluble fatty acids 

 are allowed to drain in a cool place until practically dry. A convenient 

 filter stand for both filtration and draining is illustrated by Wiley. ^ The 

 small particles of fat adhering to the filter are dissolved in ether in a con- 

 tinuous fat e.xtractor ^ rim into the flask, and the ether expelled in the usual 

 manner. The ether fumes are very persistent and necessitate blowing 

 out the flask vnth. hand bellows. The insoluble acids are dried in an oven 

 at 100° C, or in a vacuum oven at 70° C, to approximately constant 

 weight. At 100° C. the diying periods should not exceed two hours. The 

 weight of the flask is determined at the completion of the test, to offset 

 the solvent action of the reagents on the glass. Blanks should be run on 

 every new lot of ceresine to determine the amount (if any) of soluble 

 raaterial present. 



There are compensating errors that usually result from tliis method, 

 namely, volatihzation of fatty acids, dehydration of simple and of hydroxy 

 fatty acids with the formation of anhydrides and of lactones, respectively, 

 and oxidation of unsaturated acids. * Drying in a vacuum oven at 70° C, 

 in a current of carbonic acid gas or even of dry air, will reduce oxidation 

 as well as dehydration and volatilization. 



Limit of error, 0.25 per cent. 



Synopsis of Reaction. — Similar to those of Reichert-Meissl number. 



Swp-plementary Notes. — Differences in chemical structure of the insolu- 

 ble fatty acids permit of their classification into saturated, unsaturated, 

 hydroxy acids, etc. 



The principal saturated acids are lauric, myristic, palmitic, stearic, 

 arachic and dihydroxystearic. 



The most prominent unsaturated acids are oleic, erucic, linolic, lino- 

 lenic, clupanodonic and ricinoleic. When these acids are compared with 

 the empirical formula for saturated acids, CjiH2 n+iCOOH, they show a 

 deficiency of 2, 4, 6 or 8 atoms of hydrogen, which indicates their power 

 to absorb iodine chloride with the formation of additive compoimds. 



' The amount required varies with the consistency of the insoluble acids that are being deter- 

 mined. 



> Foods and Food Adulterants, U. S. Dept. Agr., Bur. Chem., Bui. 13, p. 457. 



' See Fig. 4, page 136. 



* Saturated acids do not readily absorb oxygen. Unsaturated acids of the linolic and linolenic 

 series absorb oxygen from the air at ordinary temperatures, and of the oleic series at higher tem- 

 peratures. 



