CHAP. VII.] 



THE CONNECTIVE TISSUES. 



267 



With the aid of the appended table based upon the observations 

 of Heintz * an approximate estimation of the composition of a mixture 

 of stearic and palmitic acids can be made. 



A mixture of 



In order to demonstrate the separate presence of stearic and palmitic 

 acid it is, however, essential to proceed further. The mixture of the 

 acids is dissolved in boiling alcohol and treated with sodium carbonate, 

 then evaporated to dryness on the water- bath ; the residue is further 

 heated in the air-bath to 130. The residue is pulverized and boiled 

 with absolute alcohol ; the solution is filtered hot. 



Fractional This solution is now subjected to fractional precipita- 



precipitation tion, by adding either solution of chloride or acetate of 

 of a mixture barium. "When one of these salts is added, little by little, 

 of fatty acids. ^ o a solution containing both stearic and palmitic acids, the 

 precipitate which first falls is composed entirely of barium stearate ; 

 the further gradual addition of the barium salt leads to the precipi- 

 tation of a mixture of barium stearate and palmitate, and if the addition 

 of barium salt be continued after this pure barium palmitate falls. 

 Relying upon these facts the experimenter adds to the alcoholic solu- 

 tion of the mixed fatty acids one or two drops of a solution of barium 

 chloride or acetate, filters, heats the filtrate to boiling, then adds to it 

 one or two drops more of the barium solution, collects the new precipitate 

 on a separate filter, heats the filtrate, and repeats these operations until 

 the addition of barium salt occasions no new precipitate. Each precipitate 

 is collected on a separate small filter, is washed with warm alcohol 

 and dried at 120C. The barium in each precipitate is then determined 

 by igniting in a porcelain capsule, and adding first hydrochloric and 

 then sulphuric acid to the ash, again igniting, and weighing the barium 

 sulphate. If stearic acid is present the first precipitates should contain 

 the amount of barium corresponding to barium stearate; if palmitic 

 acid, the last precipitates should agree in composition with barium pal- 

 mitate. 



Comftosition of the barium salts of stearic and palmitic acids. 



100 parts of barium stearate contain 19-49 parts of barium. 

 palmitate 21 '17 



1 Poggendorff's Annalen, Vol. xcn. p. 588. 



