816 EXPERIMENT STATION BECOBD. 



ated over practically the whole range of water content dealt with iu the experi- 

 ments, one expressing the effect of the gradually diminishing water surface on 

 evajmration and the other giving an empirical measure of the influence of the 

 vapor pressure of the moist soil. The following equation for rate of evapora- 

 tion from soil was developed : 



^^=^/^+lV2.303 \o{r,„{w+K)-]ogeK], where ^=rate of evaporation. 



i(;=pereentage of water present by weight. 



s=specitic gravity of the soil. 



A and A'=constants. 



Partial sterilization of soil by volatile and nonvolatile antiseptics, W. 

 BunmN {Jour. Agr. Sci. [IJtigland], 6 (191J,). No. J,, pp. J,n-J,5L fiys. 4).— 

 Supplementing previous experiments by Russell and IIutchins<^)n and others 

 (E. S. R., 31, p. 27) further tests were made by the Russell and Hutchinson 

 method on two soils, one high and the other low in nitrates, to compare a 

 wider range of substances including benzene, toluene, cyclohexane, pentane, 

 hexane, heptane, chloroform, ether, acetone, formaldehyde, alcohols, phenol, 

 cresol. hydroquinone, pyridin, calcium sulphid, sulphur, sulphur dioxid, .sodium 

 fluorid, and .sodium chlorid. The object of these tests was to determine whether 

 the phenomena observed in the earlier experiments in the case of toluene and 

 a few other substances are generally true of antiseptics, including (1) those 

 which are completely volatile and disappear entirely from the soil when their 

 work is done and (2) those which remain in the soil for a considerable time 

 or else leave decomposition products and so exert a prolonged action upon the 

 bacterial flora of the soil and upon the plant. 



It was found that the characteristics of true partial sterilization are com- 

 mon to a large number of antiseptics, and consist in an initial decrease in 

 bacterial numbers followed by a large sustained increase, the killing of pro- 

 tozoa and nitrifying organisms, an initial increase in ammonia followed by a 

 considerable increase in the rate of ammonia production, and no change in 

 the results obtained following an increase in the dose in any pai'ticular chemi- 

 cal when once true partial sterilization has taken place. True partial steriliza- 

 tion w^as obtained only with the easily volatile or removable antiseptics, the 

 dose of the more important of these necessary for this purpose being as fol- 

 lows: Benzene, below 0.15 per cent by weight of dry soil; toluene, 0.09; cyclo- 

 hexane, 0.17 ; pentane, 0.7 ; hexane, 0.17 ; heptane. 0.1 ; chloroform, below 0.24 ; 

 ether, below 1.5 ; and acetone, 5.8. 



" Substances not completely removable from the .soil have some lasting influ- 

 ence on the flora. With the weaker doses two or three special species of bac- 

 teria characteristic of the chemical used multiply temporarily to an enormous 

 extent, but the organisms do not produce ammonia, consequently there is no 

 gain in ammonia and nitrate as the result of their action. The higher doses 

 permanently suppress all microbiological action in the soil. 



" It appears to be a general rule that a simple flora can attain extraordinarily 

 high numbers, while a complex flora, such as prevails after normal partial 

 sterilization, does not attain to higher numbers than the comparatively low 

 level of about five times those in the untreated. 



" It is possible to trace a certain relationship between the action of all the 

 substances used. The intensity of the effects shades off gradually from that of 

 the powerful nonvolatile antiseptics through cresol and formaldehyde to the 

 more and less potent volatile anti.septics respectively, till finally the action of 

 merely spreading out the soil iu a thin layer is reached [see abstract below]." 



