322 EXPERIMENT STATION RECORD. 



Summarizing tlie results, the author states that " soils not only have the 

 power of adsorbing dissolved salts from solutions, but also of adsorbing one ion 

 at a greater rate than the other, or selectively adsorbing, to a marked extent. 



"The presence of bases of the soil (Ca, Mg, etc.) in solution after shaking 

 certain salt solutions with or percolating through a soil is probably not due to 

 a direct chemical reaction of the salt in solution with the silicates of the soil, 

 but to a reaction of free acid, resulting from a selective adsoi-ption of the 

 cation with the mineral components of the soil. 



" The rate of adsorption of chlorin ions from solution by soils is much less 

 than of potassium ions. The selective adsorption of potassium from a potas- 

 sium-chlorid solution by a soil increases in amount with the concentration up 

 to a certain point and then remains practically constant. The percentage of 

 potassium adsorbed from a potassium-chlorid solution increases asymptotically 

 as the concentration of potassium chlorid decreases and at very low concentra- 

 tions adsorption is practically complete. In general, the smaller the soil par- 

 ticles the greater the selective adsorption of potassium from a potassium-chlorid 

 solution by the soil. 



" The presence of sodium nitrate decreases the adsorption of potassium from 

 a solution of potassium chlorid by a soil up to a concentration of about 37.5" 

 gm. of potassium chlorid per liter and then increases it. The presence of 

 monobasic calcium phosphate does not change appreciably the adsorption of 

 potassium from a potassium-chlorid solution by a soil. 



" Finally, if a mineral fertilizer be applied to a soil and exposed to the rain 

 and thus dissolved and carried through the soil in solution, these substances 

 will be adsorbed (an entirely physical phenomenon) either as a whole or se- 

 lectively from the solution by the vast surface of the soil particles and will be 

 held there by this same physical force until the plant or subsequent leaching 

 removes it. The presence of other mineral substances added to the soil may or 

 may not increase or decrease the rate at which this adsorptive phenomenon 

 takes place." 



The inactivity of the soil protozoa, R. Gkeig-Smith {Proc. Linn. Soc. N. 8, 

 Wales, 37 (1912), pt. 4, pp. 655-672, figs. 7; ahs. in CenthJ. Bakt. [etc.'], 2. AU., 

 39 {1913), No. 4-7, p. 152). — In these investigations, continuing previous work 

 (E. S. R., 28, p. 623), the author endeavored to test the action of the soil 

 phagocytes (1) by adding them purposely to soil, and (2) by using the extracts 

 of raw soil, as was done by Russell and Hutchinson, taking care to use soil that 

 had not been overheated and to have controls of unfiltered soil extracts to com- 

 pare with the filtered, presumably protozoa-free, extracts. 



It is concluded from the experiments as a whole " that Russell's contention 

 can not be sustained ; the protozoa have little or no action in limiting the num- 

 ber of soil bacteria." 



It was found that the larger ciliates, such as Colpoda cucullns, were not 

 destroyed when comparatively large amounts of volatile disinfectant were 

 added to the soil. " Upon adding suspensions of protozoa, there was no evi- 

 dence of any limitation in the numbers of the soil bacteria. Any enhanced 

 effect was due to the addition of the bacteria contained in the suspensions. 

 The filtration of a soil extract had no influence, beyond that of removing some 

 of the bacteria in the suspension. Any phagocytic tendencies that the soil pro- 

 tozoa possess have no influence in limiting the numbers of bacteria in the soil. 

 So far as the growth of bacteria is concerned, the effect of heat is of a different 

 character from that of a volatile disinfectant. Inferentially, the toxins and 

 nutrients of the soil are alone concerned with the changes that occur when soils 

 are heated or treated with volatile disinfectants." 



