188 EXPERIMENT STATION RECORD. 



of carbonate suffices to destroy the solvent action of a large quantity of 

 acid. This lact was verified in a long series of experiments with phos- 

 phates of very different origin and variable content of carbonate of lime. 



The author's observations confirm those of Deh^rain as regards the 

 presence of free acetic acid in peaty soils. He found an amount of this 

 acid in a soil of this class corresponding to about 7 gm. of acid per kilo- 

 gram of soil. Comparisons of the solvent action of this acid on the 

 phosphates with that of citric acid showed that acetic acid dissolved 

 the phosphoric acid less readily than the citric acid, but that in this 

 case also the carbonate of lime interfered to a consideral)le extent with 

 the solution of the phosphates. 



The solvent action of carbonic acid on phosphates was also studied, 

 with the result of showing that this acid does not dissolve phosphoric 

 acid to any great extent, but readily dissolves the carbonate of lime, 

 and in this way facilitates the solution of the phosphate of lime l)y the 

 other acids of the soil. 



In conclusion, it is urged that in judging of the quality of a phosphate 

 the assimilability of phosphoric acid in weak acids, as well as the con- 

 tent of carbonate of lime, should be taken into consideration. 



A simple method of v/orking up molybdic residues, and some 

 suggestions regarding the determination of phosphoric acid by 

 the molybdic method, II. Borntrager {ZUchr. amdyt. Chem., 33 

 {1891), No. 3, pp. 341-343). — The method proposed for working up the 

 molybdic residues is as follows: Both the acid and ammoniacal filtrates 

 obtained in the determination of phosphoric acid by the molybdic 

 method are poured into a large, wide-necked fiask containing 250 cc. 

 of ammonia solution. Immediately, or in a short time, pure molybdic 

 acid sei^arates out in the form of fine needles. "When the flask is 

 nearly full the solution is made almost neutral and allowed to stand. 

 It is then filtered, the precipitate washed once, and pressed out. This 

 precipitate is dissolved in the snuillest possible quantity of ammonia, 

 the solution filtered quickly to free it from silicic acid, magnesia, etc., 

 and the filtrate diluted with water to a sp. gr. of 1.11 (14° Be.) at 17° 

 C. Such a solution contains exactly 150 gm. of molybdate of ammonia 

 per liter. To 1 liter of the solution the author adds 1 liter of nitric acid 

 of 1.2 sp. gr., allows the yellow ijrecipitate of traces of phosphoric acid 

 present to subside, ami uses the sui)ernataut solution in the determina- 

 tion of i^hosphoric acid. 



In the author's opinion it is not desirable to obtain the* alnmonlum- 

 maguesium phosphate in crystalline form, and to prevent this he adds 

 to the ammonia solution of the yellow precipitate fuming hydrochloric 

 acid until the precipitate formed does not immediately redissolve. 

 The addition of this acid causes the solution to become very hot, which 

 favors precipitation. Magnesia mixture is added to the hot solution 

 and the precipitate filtered off as soon as gas bubbles, begin to rise 

 from the precii)itate, which is usually m from 1 to 2 hours. 



