DETERMINATION OF MALIC ACID. 



negligible. This procedure pro VIM! satisfactory and no further diffi- 

 culty was experienced in this direction. 



A number of experiments were made to determine what effect, if 

 any, is produced by an excessive amount of uranyl acetate. The re- 

 sults all showed that such an excess does not influence the rotation of 

 the solution. On the other hand, it is quite possible to add too small 

 an amount of the salt to the solution under examination. In the case 

 of solutions containing a comparatively large amount of malic acid, 

 several hours may elapse before a maximum change in rotation is ob- 

 tained. To test this point a solution containing 2.94 per cent of malic 

 acid as sodium malate was treated with an excess of uranyl acetate, 

 shaken frequently and polarized at intervals. The polarizations ob- 

 tained were as follows: 



oy 



. After 10 minutes 60.4 



35 minutes 68.7 



1 hour.! 74.1 



2 hours, 10 minutes 82.0 



2 hours, 45 minutes 82.8 



4 hours, 10 minutes 83.0 



This indicates that after two hours the reading is practically con- 

 stant, since a difference of 1 corresponds to only 0.036 per cent of 

 malic acid. It must be remembered, however, that frequent agitation 

 is also needed if a maximum is to be attained in this time. 



An approximate determination of the solubility of uranyl acetate 

 at ordinary temperatures gave the following results: 



Grams per 

 100 cc. 



1. In water 8.5 



2. In a solution containing 1.25 per cent of malic acid as sodium malate 11. 96 



3. In a solution containing 2.5 per cent of malic acid as sodium malate 13. 32 



REMOVAL OF THE MALIC ACID. 



TTalden reports [a] D for a 0.65 per cent solution of Z-malic acid 

 as approximately 0.77 circular degrees, as compared with 475 

 (circular) for the uranium complex. It is evident, therefore, that in 

 ordinary concentrations the rotation of free malic acid is negligible. 

 However, as has been said, it is sometimes necessary to remove the 

 malic acid from the solution before making reading (2) for the reason 

 that the addition of uranyl acetate causes a decrease in the rotation of 

 strong sugar solutions. 1 To determine the extent of this effect, 13 

 grams of uranyl acetate were added to 100 cc of various sugar solu- 

 tions and allowed to stand one hour with frequent shaking. The so- 



1 Rembach and Weber (Zts. physikal. Chem., 1905, 51:491) have noticed that uranyl 

 nitrate produces a slight increase in the specific rotation of solutions of dextrose and 

 levulose containing 7.2 grams of the sugar in 100 cc of solution. 



