Febeuaet 10, 1911] 



SCIENCE 



225 



where it cools the metallic parts with which it 

 has contact, and by so doing induces strains 

 which complicate the problem of boiler main- 

 tenance. Moreover, a locomotive which is thus 

 filled is not in good condition for the start, 

 notwithstanding the fact that the gauge may 

 show full working pressure; for at the start 

 there is imposed upon the boiler the double 

 task of supplying steam and of raising to the 

 maximum temperature of the boiler the water 

 which was fed into it during the stop. The re- 

 sult is that the boiler pressure soon falls, and 

 considerable time is required in which to re- 

 store it. 



F. M. Goss 

 University of Iujnois 



SOIL PRODVCTIVITY 



In a discussion of the " Secular Mainten- 

 ance of Soils " before the Geological Club of 

 the University of Chicago on January 9, 

 the undersigned expressed views as follows : 



That the era of soils began at an early but 

 indeterminate period in the history of the 

 earth; that the Proterozoic lands were prob- 

 ably mantled by soils and clothed with vegeta- 

 tion ; that soils certainly prevailed on the land 

 in the Paleozoic era; that sufBcient soils and 

 vegetation mantled the earth through all later 

 eras to support the continuous evolution of 

 land life; that the total eon of productive soils 

 may be assigned a period of at least tens of 

 millions of years ; that therefore there must be 

 some efficient natural process for the main- 

 tenance of soils. 



That the origin of the soil body lies chiefly 

 in the granulation of rock; that soils are 

 wasted at the surface by wind and wash; that 

 wind and wash also distribute granules and 

 mis soils and give to nearly all soils some of 

 the essential soil constituents ; that progressive 

 granulation of rock adds soils below; that 

 progressive solution removes soil matter from 

 soils and from the rock beneath; that by these 

 composite processes the body of the soil is at 

 once enriched and impoverished; that so long 

 as the body of the soil is maintained, any 

 impoverished or anemic condition that may 

 arise can be rectified; but if the hody be lost, 



its restoration is tedious, laborious, or ex- 

 pensive. 



That the film-water that surrounds the 

 granules of the soil when in a normal moist 

 state is the specific soil water; that this is to 

 be distinguished from the ground water that 

 lies below the water-table, though these grade 

 into one another; that the soil swells with the 

 grovTth of the films in thickness; that there is 

 an optimum of film-water when the soil is 

 most swollen; that addition of water beyond 

 the optimum destroys the surface tension of 

 the films and leads to the shrinkage of the 

 soils, the packing of the granules and to un- 

 productivity ;^ that the solutions in the film- 

 water are formed with facility because of the 

 greatness of the surface contact relative to 

 volume; that the concentrations of the solu- 

 tions are controlled by the laws of equilibrium.^ 



That the soil air is inversely proportional to 

 the soil water approximately; that the soil air 

 is to be distinguished from the earth's atmos- 

 phere, though grading into it and inter- 

 changing with it through difEusion and soil 

 breathing; that, occupying the spaces between 

 the film-coated granules of the soil, the soil 

 air has great relative contact; that it acts at 

 special advantage on both films and granules; 

 that the union of minutely granulated earth, 

 film-water under tension and interstitial air 

 gives a combination of exceptional solvent and 

 reactive power. 



That the soil is the home of minute life, 

 plant and animal; that these intensify and 

 modify the inorganic activities ; that the forms 

 of life are with little doubt more or less pre- 

 datory and parasitic on one another; that 

 these relations are probably in some cases 

 pathogenic, and that these give rise to unsani- 

 tary states of the soil which affect its product- 

 ivity; that progress is being made by Whitney 

 and his associates in the discovery of toxic 

 exudations that affect productivity; that plant 

 societies are perhaps in part a result of mutu- 

 ally beneficial relations in respect to exuda- 

 tions and by-products; that the soil thus is 

 little less than a world in itself; that its 



^Cameron, Journal Physical Chemistry, 1910. 



' Cameron, loo. (At. 



