AGRICULTURAL CHEMISTRY AGROTECHNY. 409 



Two methods of separation of the metals of the alkaline-earth group, 

 Alice G. Patekson (Jour. Amer. Chcm. Soc, 37 {1915), No. 10, pp. 2346-2352). — 

 The methods devised are based on the slight differences in solubility of the 

 relatively insoluble salts of the group, both being applications of the principle 

 involved in fractional precipitation. If two or more precipitating agents are 

 added to a solution containing a mixture of salts, any given metallic ion will 

 unite with that acid ion which forms the least soluble salt. 



Detailed procedures for the qualitative separation of the alkaline-earth 

 metals, based on the above principle, are given. It is thought that the principle 

 may have a wider application in general analytical work and may perhaps be 

 valuable for quantitative separations. 



Nephelometric estimation of phosphorus, P. A. Kodee and G. Egeker (Jour. 

 Amer. Chcm. Soc, 37 {1915), No. 10, pp. 2373-2381, figs. 2).— The reagent of 

 Pouget and Chouchak (E. S. R., 20, p. 703; 21, p. 105) for the estimation of 

 phosphorus has been so modified by the authors as to be stable, colorless, and 

 both quantitatively and nephelometrically applicable. The preparation of re- 

 agents and detailed procedure for the estimation of phosphorus is described. 

 The authors have shown that 0.005 mg. of phosphorus in 10 cc. of solution, or 1 

 part in 2,000,000 parts of water, is easily determined quantitatively with the 

 nepheloraeter (E. S. R., 30, p. 410). The method, as a rule, is applicable directly 

 to any solution containing phosphates but no organic matter, provided the solu- 

 tion is neutral or slightly acid and not turbid. 



• On the accuracy of Neumann's method for the estimation of phosphorus, 

 H. S. H. Waedlaw {Jour, and Proc. Roy. Soc. N. S. Wales, 48 {1914), pt. 1, 

 pp. 73-93). — After a critical study of the possible sources of error in Neumann's 

 method for the estimation of phosphorus, the author concludes that the values 

 obtained in the estimation of phosphorus are always high. The error increases 

 with the amount of phosphate estimated, and its source is an excess of molyb- 

 denum carried down in the precipitate of ammonium phosphomolybdate. The 

 error is independent of the rate of addition of the precipitant or the time of 

 contact between the px'ecipitate and the mother liquor, and it can not be reduced 

 by lowering the temperature of precipitation, as this leads to incomplete pre- 

 cipitation. 



On the factor to be used for the calculation of the phosphoric acid in Neu- 

 mann's method; the factor as influenced by the water used for washing the 

 yellow precipitate, S. L. Jodidi and E. H. Kellogg {Jour. FranlcUn Inst., 180 

 {1915), No. 3, pp. 349-367). — The authors have shown that the factor used for 

 the calculation of phosphoric acid in Neumann's method is to a degree influenced 

 by the amount of water used for washing the ammonium phosphomolybdate. 

 Losses of from 1.07 to 3.95 per cent of the phosphorus employed were observed 

 when washing the yellow precipitate with four successive portions of 150 cc. 

 each of ice-cold water. By washing the precipitate with but three portions of 

 50 cc. each the losses were smaller, ranging from 0.89 to 3.2 per cent, and this 

 procedure is recommended. The more material used in the method the smaller 

 was the percentage of phosphorus lost in the filtrate and washings. Analytical 

 data indicate that the ammonium phosphomolybdate is not absolutely insoluble 

 in the liquid from wliich it is precipitated, the losses ranging in the experiments 

 reported from 0.4 to 0.77 per cent of the phosphorus employed. 



It has been found to be more convenient to use a 300-cc. round-bottom flask 

 than a 500 to 750 cc. flask for the formation of the yellow precipitate. A large 

 flask, however, is necessary for the oxidation of organic matter if such be 

 present. 



See also a previous note (E. S. R., 33, p. 803). 



