12 EXPERIMENT STATION RECORD. 



to readily absorb, filter, and store tlie rain water, and tbus to furnisli larj^e 

 ciiiantities of very ])ure water. 



A study of the process of nitrification with, reference to the purification of 

 sewage, HAKKitTTE Chick (Proc. Roij. Soc. [Loiidon], >Scr. B, 7? {1906), No. 

 n J/7, pp. 241-266, fig. 1; abs. in Jour. Chem. Soc. [London], 90 (1906), No. 522, 

 li p. 245). — The process of nitrification was studied in experimental laboratory 

 filters acting both as continuous filters and contact beds. It was found that 

 nitrification of ammonia during sewage purification occurred in two stages due 

 to activity of two distinct classes of bacteria, one producing nitrites and the 

 other oxidizing the nitrites to nitrates. These bacteria exist not only in the 

 substance of the filter, but are also carried away in large quantities in the fil- 

 trates. They belong to tlie same group as those producing nitrification in the 

 soil. The action of the organisms producing nitrates may be retarded when 

 the sewage is strongly anuiioniacal. 



Tbe ability of the nitrifying organisms to live and work in sewage filters so 

 highly charged with organic matter is discussed. This is ascribed to (1) the 

 presence of organisms in symbiosis with the nitrifying organisms, rendering 

 the latter more resistant; (2) the retention of the organic matter in large part 

 near the surface of the filters; and (:>) the presence of very large numbers of 

 nitrifying organisms in the filters. 



The influence of temperature on the oxidation of sewage was studied, and it 

 was observed that the efficiency of the filters and the rapidity of the process of 

 oxidation were greatly increased by raising the temperature. In any case 

 nitrification was extremely rapid, being completed during the time required for 

 percolation, 2 to 3 hours. The continuous filters were more efficient than con- 

 tact Iteds in purifying the sewage. 



The purification of sewage, W. Ramsay {Osten: Vhcvt. Ztg.. 9 {1906), No. 

 10, pp. 135-139). — This is a paper which was presented before the Sixth Inter- 

 national Congress of Applied Chemistry, Rome, 190G, which discusses the loss of 

 fertilizing matter, particularly nitrogen, in sewage, and the various methods of 

 sewage disposal which have been proposed. The difliculties in the way of the 

 successful use of the irrigation method alone are pointed out. 



SOILS— FERTILIZERS. 



Some peculiarities of rock weathering and soil formation in the arid and 

 humid regions, E. W. Hilgard {Aiiici: .four. Sci.. //. scr.. 12 {1906). No. 12Jf, pp. 

 261-269). — The author summarizes in this a.rticle his (tbservations and con- 

 clusions regarding various phases of this subject, especially as regards soil 

 formation, which have been recorded in various previous publications. It is 

 made clear that tbe processes of soil formation in arid regions are very different 

 from those oi)eratiiig in humid regions and show " the need of caution in ai)ply- 

 ing tbe maxims of tbe humid region in arid climates." 



On the changes which minerals undergo in cultivated soil, T. Bieler {Bui. 

 Soc. Nat. Af/r. Fniiicc, 66 (19116), No. 2, pp. 1S6-195). — The author pre.sents evi- 

 dence to show tliat the solution of silicates in the soil is a very complex and 

 gradual process, resulting in partial or total decomposition of these compounds 

 under the action of various factors working in association. Among these factors, 

 which are enumerated and discussed, are chemical decomposition, and the solvent 

 action of air and water, of organic matter, roots, and micro-orgiinisms. 



The wire-basket method for determining the manurial requirements of 

 soils, F. D. Gardner (i\ S. Dept. Agr., Bur. Soils Circ. IS, pp. 6. figs. 2). — The 

 metbdds of constructing the wire baskets and of using them in determining the 

 manurial requiremcuts ot' soils are described (.see E. tS. K., 17, p, 227), 



