RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



A volumetric citrate method for quick and exact determina- 

 tion of phosphoric acid in superphosphates, S. Littman (Chan. 

 Ztg., 22 (1898), No. 68, pp. 691, 692).— The method proposed is as fol- 

 lows: Dissolve 10 gm. of superphosphate in h liter of water, shake £ 

 hour, and filter. To 50 cc. of the filtered solution add methyl orange 

 and run in ^ normal soda solution until a distinct yellow color appears, 

 showing that the free phosphoric acid, H 3 P0 4 , has been converted into 

 inonosodium phosphate, which reacts alkaline with methyl orange and 

 acid with phenolphthalein. Add 10 cc. of neutral sodium citrate solu- 

 tion, prepared by exactly neutralizing a solution of 30 gm. of sodium 

 hydrate in 120 cc. of water with pure concentrated citric acid, allow to 

 stand 24 hours, filter, and dilute to 250 cc. This converts the unaltered 

 monocalcium phosphate into monosodium phosphate. Phenolphthalein 

 is then added, and soda solution run in until a red coloration appears, 

 showing that the monosodium phosphate has been converted into triso- 

 cbium phosphate. The number of cubic centimeters of soda solution 

 required for this purpose multiplied by 0.71 gives the percentage of 

 phosphoric acid. 



This method and the gravimetric method were compared with very 

 satisfactory results in a series of determinations of phosphoric acid in 

 superphosphates made from Florida and Algerian phosphates, bone 

 meal, and bone ash, and in spodium and mixed fertilizers. The aver- 

 age difference in 50 determinations by the two methods was 0.13 per 

 cent. 



On a new method of determining nitric acid, W. Ackermann 

 (Chem. Ztg., 22 (1898), No. 68, pp. 690, 691).— The method proposed is 

 based upon the observation made by Kuhlmann l that ferrous hydrate 

 heated with a nitrate solution is transformed into black oxid with evo- 

 lution of ammonia. The details of the method are as follows: Place 

 about 1 gm. of the nitrate in a half-liter flask with 30 cc. soda solution 

 of 1.33 sp. gr. and 40 gm. of iron sulphate dissolved in water. The vol- 

 ume of solution should be about 160 cc. The iron sulphate solution is 

 prepared by dissolving 308 gm. of the sulphate in 1 liter of water. 



'Gmelin-Kraut, 3, p. 301. 



513 



