2 DETERMINATION OF MALIC ACID. 



the American Chemical Society in July, 1910, and contains the 

 results of a large amount of work. The method outlined depends 

 on the use of a uranium salt, but in other respects it differs mate- 

 rially from the one here proposed. With this exception, no one 

 appears to have attempted the quantitative determination of malic 

 acid by treatment with uranium. 



THE METHOD IN BRIEF. 



The method in brief consists in treating a portion of the neutral- 

 ized 1 solution containing malic acid with uranyl acetate and polar- 

 izing it. The algebraic difference between the reading so obtained 

 and that of the untreated solution is multiplied by the factor 0.03G 

 to obtain the percentage of malic acid present. With the exception 

 of d-tartaric acid, none of the common optically active substances 

 interfere with the determination, and consequently they need not be 

 removed. Uranyl acetate slightly decreases the rotation of sugars. 

 This may give rise to an error in the estimation of small amounts 

 of malic acid in the presence of large amounts of invert sugar. 

 Hence, when the rotation of the original solution is negative and the 

 approximate amount of sugar or malic acid is unknown, or when 

 more than 10 per cent of reducing sugars and less than 0.25 per cent 

 of malic acid are present, it is necessary to precipitate the malic acid 

 and treat the filtrate with uranyl acetate also. In this case the 

 polarization of this filtrate, instead of that of the untreated solu- 

 tion, is subtracted from the polarization of the solution containing 

 both malic acid and uranyl acetate, and the difference is multiplied 

 by 0.036. 



DETAILS OF THE METHOD. 



Dilute a measured volume of the solution, usually 10 cc, with 

 quite a large volume of water, add phenolphthalein, and titrate with 

 standard alkali to a decided pink color. Transfer another measured 

 portion of the solution (75 cc is a convenient volume) to a 100 cc 

 graduated flask, and add enough standard alkali, calculated from the 

 above titration, to neutralize the acidity. A slight excess of alkali 

 is not objectionable. If the solution is dark colored, add 5 or 10 cc 

 of alumina cream. Dilute to the mark, mix thoroughly, and filter 

 if necessary through a folded filter. 



(1) Treat about 25 cc of the filtrate with powered uranyl acetate, 

 adding enough of the salt so that a small amount remains undissolved 

 after two hours. Two and one-half grams of uranyl acetate will 

 usually be sufficient, except in the presence of large amounts of 

 malic acid. In case all the uranium salt dissolves more should be 

 added. Allow the mixture to stand for two hours, shaking fre- 



1 If no mineral acids are present it is not necessary to neutralize the malic acid. 



