12 DETERMINATION OF MALIC ACID. 



TABLE VI. Malic acid determinations on unknown solutions. 



i Determinations by C. W. Clark. 

 SUMMARY. 



(1) When a neutralized solution of malic acid is treated with 

 uranyl acetate, its rotation is increased approximately 28 V. for each 

 per cent of malic acid in the solution; ^-tartaric acid is the only 

 other common acid which is affected in this way by uranyl acetate, 

 Hence, in the absence of 6?-tartaric acid, malic acid may be deter- 

 mined quantitatively by treating its solution with uranyl acetate, 

 polarizing, and multiplying the difference between this reading and 

 that of the untreated solution by 0.036. The product equals the per- 

 centage of malic acid present. 



(2) In the presence of more than 10 per cent of reducing sugars 

 and less than 0.25 per cent of malic acid, the results may be affected 

 by the action of uranyl acetate on the rotation of the sugar. Hence, 

 in this case or when the amounts of sugar or malic acid are unknown, 

 certain simple modifications are necessary. 



(3) For this determination, the most favorable limits of concen- 

 tration of malic acid are between 0.2 to 2.5 per cent. The percentage 

 error seldom amounts to more than 5 per cent of the malic acid 

 present. Twelve complete determinations may easily be made in 

 four hours time, including two hours during which the solutions 

 require no treatment other than frequent shaking. 



o 



