RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



The determination of humus, F. J. Alway, E. K. Files, and R. M. Pinckney 

 {Nebraska »S*fo. Bui. 115, pp. 3-25; Jour. Indus, and Engin. Chem., 2 (1910), 

 No. 7, pp. 317-322).—" The Hilgard, Huston-McBride [E. S. R., 5, p. 510], Came- 

 rou-Breazeale [E. S. R., 15, p. 744] and Mooers-Hampton [E. S. R., 19, p. 714] 

 methods for the determination of humus were compared, using arid, semiarid, 

 and humid soils. 



" The Hilgard method as used by its author was found to give entire reliable 

 and satisfactory results. In the case of soils rich in humus and those of very 

 fine texture the method is at times very tedious. 



" The Huston-McBride or ' official ' method gives results which are entirely 

 unreliable and which, in the case of most soils, are far too high. The errors 

 incidental to the method are of such a nature that it seems impossible to apply 

 to the results any satisfactory correction formula. The humus extract obtained 

 by the Huston-McBride method, after being passed through a properly prepared 

 porcelain filter, gives results which are concordant with those obtained by the 

 Hilgard method. 



" The ftlooers-Hampton modification of the Huston-McBride method gives 

 results entirely concordant with those of the Hilgard method. For some soils it 

 is preferable to the latter, requiring much less time. 



"Ammonia solutions of different strengths were not found to have the same 

 solvent power for humus. The differences for strengths between 2 and 8 per 

 cent were slight, but where solutions of from 16 to 28 per cent \^ere used consider- 

 ably more humus was dissolved. 



" The amount of so-called ' humus ash ' found in the case of a soil sample varies 

 from method to method and bears no relation to the strength of the ammonia 

 used. There is little or no agreement between duplicate determinations of the 

 'humus ash.' From 4 to 38 times as much ash is obtained by the Huston- 

 McBride method as is obtained by tbe other methods. It is probable that the 

 greater portion of the ' humus ash ' obtained by any of the methods is not an 

 essential part of the humus. In reporting the humus the percentage of ' humus 

 ash ' should always be reported, as it serves as an indication of the reliability 

 of the humus determination." 



The determination of phosphoric acid by means of standard silver nitrate, 

 J. M. WiLKiE (Jovr. Soc. Chcin. Indus., 29 (1910), No. 13, pp. 79^-796).— The 

 method is carried out as follows : 



To the phosphoric acid solution phenolphthalein is added and then strong 

 sodium hydrate solution until just a pink color is obtained. This color is then 

 removed with nitric acid added dropwise. When calcium is present no special 

 indicator is required, as the precipitate of calcium phosphate serves the purpose, 

 and the nitric acid is added until solution has taken place. After adding an 

 excess of standardized silver nitrate solution, 10 cc. of a nearly decinormal sodium 

 acetate solution is added, and then a dilute igodium hydrate solution (approxi- 



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