AGRICULTURAL CHEMISTRY AGROTECHNY. 805 



and leaves beliiml a black powder resembling platinum black. This is dis- 

 solved in aqua regia, the resulting solution evaporated to dryness, and the 

 residue redissolved in very dilute hydrochloric acid. From this solution the 

 platinum is separated either by precipitating the metal with zinc or by 

 precipitating with hydrogen sulphid, filtering, washing, and igniting the result- 

 ing sulphid. The platinum thus obtained is readily soluble in aqua regia, and 

 easily converted into chloroplatinic acid in the usual manner. 



A possible source of error in colorimeter observations, J. H. Long (Jour. 

 Amcr. Clicm. Soc, 38 (1916), No. 3, pp. 7 16-7 IS). —The author reports certain 

 discrepancies in colorimeter observations which resulted from using an instru- 

 ment which had stood through a hot summer in a room the temperature of 

 whicli often reached 33° C. (91.4° F.). At this temperature the wax by which 

 the prisms are fastened in their brass sockets becomes soft enough to permit 

 the slow displacement of the glass. Care should therefore be exercised to keep 

 instruments away from the vicinity of steam radiators and from places which 

 are likelj' to become very warm in summer. 



An evaluation of the methods for the determination of phosphoric acids 

 soluble in citric acid and that found in dephosphorization slags (Thomas 

 slag), O. SiCHMANN (Zhur. Opyfn. Agroii., 16 (1915), No. S, pp. 169-212).— As 

 the result of a critical comparison the author has found very little difference 

 between the molybdic method, the methods of Lorenz (E. S. R., 13, p. 14), 

 Topp (E. S. R., 29, p. 410), Darmstadt, and Naumann (E. S. R., 14, p. 940), 

 and the hydrochloric acid method. The Lorenz method gave the lowest results. 

 For convenience and rapidity the methods of Popp and Lox'enz are recommended, 

 the latter being the simpler. 



Easily extractable phosphorus and phosphorus nutrition, I. Jakouchkine 

 (Zhur. Opvtn. A(jron., 16 (1915), No. 2, pp. llS-139) .—The author has shown 

 that for material poor in fat, such as stems or stalks, the alcohol and ether 

 extraction does not cause an appreciable decrease of phosphorus pentoxid in 

 the acid extract. Direct precipitation in citric acid was used in separating 

 the mineral phosphate from the phytin. More exact results may be obtained 

 by using this method in combination with that of IwanofE by first precipitating 

 with magnesia mixture in tlie presence of citric acid, and, after dissolving in 

 nitric acid, reprecipitating by Neumann's method. 



The amount of phytin in the grain is apparently dependent on the condition 

 of the soil. The fertility of the soil is indicated by the mineral-phosphate 

 content of the straw, and when the content is less than from 0.07 to 0.1 per 

 cent a phosphate fertilizer is deemed necessary, while a mineral-phosphate 

 content greater than 0.15 per cent shows that the soil is sufficiently rich In 

 phosphorus. 



The decomposition of tetrathionates in alkaline solution as a source of 

 error in certain iodin titrations, R. M. Chapin (Jour. Amer. Chem. Soc, 3S 

 (1916), No. 3, pp. 625, 626). — The experimental data reported indicate that 

 " tetrathionates are notably sensitive to even low concentrations of hydroxyl 

 ions, though only slightly affected by sodium bicarbonate, and still less by 

 sodium bicarbonate in presence of carbonic acid. It therefore follows that 

 acid solutions containing tetrathionates, if to be later titrated with iodin or 

 subjected to any treatment involving assumption that the tetrathionate present 

 has remained unaffected, should never be neutralized by any substance of 

 distinctly alkaline properties." Sodimu carbonate, however, may be used within 

 reasonable limits of error, provided the solution is not subjected to an elevated 

 temi)erature for any length of time. Sodium sulphite is recommended as a 

 discharging agent for iodin in place of sodium thiosulphate. 



