1919] SOILS FERTILIZERS. 123 



Effects of air-clx*ying and alternate wetting and drying were so irregular, as 

 measured by dye adsorption, as to be deemed inconclusive. The immersion of 

 a soil in water for 2 years increased its adsorptive capacity for methylene blue. 

 Leaching a soil also increased its adsorption of methylene blue. Less diamin 

 sky-blue was adsorbed than of methylene blue. Ignition decreased the adsorp- 

 tion of this dye. 



Drying decreased the amount of soil that would go into suspension in dis- 

 tilled water and in 4 per cent ammonium hydroxid. Drying 32 times as com- 

 pared with one drying decreased the amount of suspended matter. 



Extractions of humus with 4 per cent ammonium hydroxid showed no effect 

 on humus due to drying, while extractions with distilled water showed an 

 increase in the solubility of the coloring matter of humus due to drying. 



Oven-drying soils previous to their standing in an excess of water increased 

 the amount of iron soluble in weak hydrochloric acid, while sterilization checked 

 the formation of this easily soluble colloidal material. 



The water-vapor-adsorption method is deemed better than the dye-adsorption 

 method for measuring the total surface of soils. Finally, it is concluded that 

 " drying a surface soil once produces as much effect on the colloidal material 

 as repeated dryings alternated with moistenings. With a subsoil there is a 

 cumulative effect due to alternate drying and wetting. Drying a soil once or 

 many times produces a change in the colloidal material from which it does 

 not immediately recover on being wetted. Drying soil affects indirectly the 

 reversibility of its colloidal condition, the changes being directly produced 

 through biological and chemical action." 



A bibliography of .58 titles is appended. 



H-ion concentration — soil type — common potato scab, L. J. Gillespie and 

 L. A. Hurst {Soil Sci., 6 (1918), No. 3, pp. 219-236, flg^. 3).— In this paper, a 

 contribution from the Bureau of Plant Industry, U. S. Department of Agricul- 

 ture, the authors describe observations made on a number of soil samples rep- 

 resenting both Caribou and Washburn loam from northern Maine. These are 

 held to indicate that an excellent correlation exists between the H-ion concen- 

 tration of the soil and the occurrence of common scab (actinomycosis) of pota- 

 toes, soils having an H-ion exponent of as low as 5.2 being found to rarely 

 produce scabby potatoes. Similar results were also secured with a few soils 

 of different origin and type. The limiting zone of the H-ion exponent for the 

 potato scab organism appeared to be approximately the same for soil as for 

 culture media as previously determined (E. S. R., 40, p. 644). 



The characteristic difference of the H-ion exponent found to exist between 

 the Caribou and Washburn loams in earlier experiments (E. S. R., 38, p. 620) 

 has been confirmed, typical Caribou loam having an H-ion exponent of about 

 4.8 and being free from scab, while Washburn loam was generally less acid and 

 usually produced scabby potatoes. It is stated, further, that a considerable 

 number of soils having the exponent 5 may be successfully grown to potatoes 

 and truck crops without liming. This indicates that exponent 7 (representing 

 physico-chemical neutrality) can scarcely be regarded in general as the so- 

 called rational end-point in lime requirement tests, no such standard end-point 

 being deemed justified without further experimental work with specific crops. 



Satisfactory methods of determining the H-ion concentration of soils both 

 coloriraetrically and electrometrically are also described. The results secured 

 in applying the two methods to a large number of soils are said to have agreed 

 within the limits of experimental error. 



A list of 23 titles comprising the literature cited is appended. 

 130002°— 19 3 



