RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



The indirect weighing of quantitative precipitates. A rapid and accurate 

 method for determining the weight of a precipitate without separating it 

 from the liquid from which it was precipitated, R. W. Tiiatciiek {Jour. Ainer. 

 Chem. Soc, 23 {1901), No. 9, pp. 644-668). — The author (li8cu,sses at some length the 

 method of determining the weight of a precipitate without separating it from the 

 sohition, and cites a number of examples of the application of the method to solu- 

 tions of chemical salts- and reducing sugars. The method is based on the fact that 

 the weight of any substance is equal to its specific gravity multiplied by its volume, 

 and, conversely, that the volume of any substance is equal to its weight divided by 

 its specific gravity. "Briefly stated, the principle upon which this new method for 

 determining the weight of quantitative precipitates is based is that if the weight of a 

 definite volume of a mixture of two substances whose specific gravities are known 

 be determined, the proportion of each which is present in the mixture may be cal- 

 culated." 



While the investigation of this method is not complete, the author believes the 

 results indicate that it is applicable in gravimetric analyses, being of easy manipula- 

 tion and shortening the time required for the determination. 



Simplification of the method of determining phosphoric acid as phospho- 

 molybdic anhydrid according to Meineke-Woy; studies on methods of 

 obtaining a pure precipitate of ammonium phosphomolybdate by means of 

 molybdic solution containing citric acid; the transformation of the 

 molybdic-magnesia method into a strictly molybdic method by the use of 

 the Wagner-Stutzer molybdic solution, A. Sevda {Chem. Ztg., J5 {1901), No. 

 72, jtp. 759-768).— Th\» article briefly reviews the work of Meineke (E. S. R., 8, p. 

 100), Woy (E. S. R., 9, pp. 321, 723), Wagner \ Stutzer"'', and others, and reports in 

 detail the results of tests of the accuracy of the molybdic method under a variety of 

 conditions. In summing up the results the author states that the only error in the 

 method of determining phosphoric acid by precipitation as phosphomolyl)dic anhy- 

 drid is the sinuiltant'ous separation of free molybdic acid, and that this error can 

 not be overcome with absolute certainty Ijy a single precipitation, using an excess of the 

 molyb<lic reagent. The separation of molybdic acid in case of a single precipitation 

 is best prevented by shaking for one-fourth hour in a rotary apparatus at room tem- 

 perature and by adding 20 cc. of 10 per cent citric acid. For solutions free from 

 iron compounds the temperature should not exceed 30° C. ; for those containing 

 iron, 20° C. In the latter case also, the solution should be filtered within 15 

 minutes after the shaking. The most practical method of freeing the precipitate from 

 free molybdic acid is to dissolve in ammonia and reprecipitate in hot solution by 

 adding dilute molybdic solution and nitric acid, washing the precipitate with hot 

 solutions (60 to 80° C. ). Under some circumstances it may be necessary to repeat 

 this process. The right amounts and concentration of the reagents are of great 

 importance. The transformation of the precipitate into anhydrid is not considered 



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