AGRICULTURAL CHEMISTRY — AGROTECHNY. 509 



The refractive index of beeswax, Ij. Peldstein ( U. 8. Dcpt. Agr., Bur. Cliem. 

 Circ. 86, lip. 3). — As tlie refractive Index of beeswax is always determined at 

 some temi^rature above 63° C, and the results reported in reference to 40°, a 

 temperature at which the beeswax is solid, the author sought to eliminate the 

 calculation to 40° by setting limits for the index at some temperature above 

 the melting point. 



The results obtained with authentic samples of beeswax, some mixtures of 

 beeswax with stearin or paraffin, or with both, show that the refractometric 

 index of pure beeswax at a temperature of 75° lies between 1.4308 and 1.4451, 

 while that obtained with adulterated samples in most instances falls below. 

 The author, therefore, recommends adopting the procedure, using 75° as the 

 observation and reporting temiierature of beeswax. 



Determination of citric acid, D. S. Pratt {U. 8. Dept. Agr., Bur. Chem. 

 Circ. 88, pp. 7). — As there has been no satisfactory method for determining 

 citric acid in the presence of other fruit acids, the author proposes one wliich 

 is also suitable for the analysis of a gi'eat variety of substances besides fruit 

 and fruit products. This method is as follows : 



" If a fruit juice is under examination, weigh 50 gm. into a beaker and add 

 110 cc. of 95 per cent alcohol to throw out the pectin bodies. After standing 

 15 minutes remove these by filtration and wash the residue with 95 per cent 

 alcohol in which citric acid is readily soluble. Dilute the filtrate with water 

 to give apiu'oximately a 50 per cent alcohol content and add enough 20 per 

 cent aqueous solution of barium acetate to precipitate the barium citrate com- 

 pletely. Stir, let stand until the precipitate partially settles, and filter. Wash 

 the precipitate thoroughly with 50 per cent alcohol to remove the greater part 

 of the sugar present. This may be done by filling the paper twice with the 

 dilute alcohol. Place the filter paper and its contents in the beaker used for 

 the precii'itatioii and dry until all alcohol is removed. If desired, the same 

 result may be accomplished by washing with ether before removing the filter 

 paper from the funnel. Add about 50 cc. of water and from 3 to 5 cc. of 

 sirupy phosphoric acid to the beaker containing the filter paper and precipitate. 

 Upon warming, the barium citrate is completely dissolved. This is the chief 

 reason for the use of phosphoric acid rather than sulphuric, which would 

 throw out barium sulphate. Filter into a 100-cc. measuring fiask and make up 

 to volume with washings from the filter paper in the beaker. This completely 

 removes the barium citrate. 



"An aliquot, estimated to contain from 0.050 to 0.150 gm. of citric acid, is 

 measured into the distilling flask. About 5 to 10 cc. of sirupy phosphoric acid 

 and 400 cc. of hot water are added. When briskly boiling, add iK)tassium 

 permanganate solution (0.5 gm. per liter), 1 to 2 drops per second, until a pink 

 color throughout the solution shows the reaction to be complete. The distillate 

 is received in a liter Erlenmeyer flask containing from 30 to 40 cc. of Denlges's 

 reagent just described. The distillation is continued until about 50 to 100 cc. 

 remain in the flask. The Erlenmeyer containing the distillate is then connected 

 with a reflux condenser, and boiled gently for three-quarters of an hour after 

 the solution tui-ns milky. Filter hot through a Gooch crucible, wash with 

 water, alcohol, and finally with ether, and dry in a water oven for half an 

 hour. The weight of the precipitate multiplied by 0.22 gives citric acid." 



Duplicate results obtained with the method generally check within from 2 

 to 3 mg. of citric acid. Some notes on the distilling appparatus best suited to 

 the method are given. 



A modification in the determination of malic acid, D. S. Pratt {TJ. 8. 

 Dept. Agr., Bur. Chem. Circ. 87. pp. 2). — The Dunbar and Bacon method 

 (E. S. R., 25, p. 715) for determining malic acid presents as difficulties "the 



