THE WASTE AND CONSERVATION OF PLANT FOOD. 215 



uiiiil)l(' to icsist the action of liowiiigf Rurfiice water. The muddy 

 charactiT of the water in all stieams bordering- on cultivated hilly lields 

 alter a heavy rain storm is a familiar instance of the tremendous 

 t'licrj^ies which are <'xerted by a heavy downpour of rain in the carrying 

 of the soil into the streams and its transportation toward the sea. 



It is not necessary to emphasize tiie fact that the a^i'icultural chemist 

 is practically p(»\verless to ]»re\"ent the surface erosion due to heavy 

 rains, but ai few pract ical lessons derived froju the a])])lica.t ion of chemical 

 <lis(^overies to the soils show how, in a certain measure, ev<Mi surface 

 erosion may he controlled, or at least reduced to a minimum by the 

 ai)plication of tlu^ })rinciples <tf culture founded upon the facts disclosed 

 by advanced science. 



The observiuii' a^yriculturist will have noticed that even in a, hilly 

 country a soil in situ underlaid by limestone is less likely to be cut up 

 by iiuilies than a soil similaily situated and deticient in carbonate of 

 lime. Th(^ n^ison of this is plain. In a soil deticient in lime the clays 

 when once brought into susi)ension by moving Avater assume a semi- 

 colloid state and remain indetinitely in suspension. Clays, on the other 

 hand, which are heavily imi)regiKited with lime salts are in a lloccu- 

 lated state, and the larger aggregates thus produced settle <puckly. 

 The result of this is that such a soil is less easily moved by water, and 

 a liehl thus treated less exposed to washing by heavy rains. 



Oni- knowledge of tlocculation and its physical and chemical results 

 is dm' largely to the investigations of Shulze, Schloesing, and llilgard, 

 and the results of their researches have shown in a most emjihatic way 

 the beneficial changes which takii place, especially in stiff clay soils, by 

 the application of lime. 



It is thus an incontrovertible fact that the surface washing of culti- 

 vated iields, especially if the}' be naturally deficient in lime, could be 

 greatly diminished and has been greatly diminished by the free api)li- 

 cation of this substance. 



The change in the physical condition of the soil, which is produced 

 l)y tlie lime, is also another important factor worthy of consider-ation. 

 A stilf clay soil is almost impervious to the i)enetration of surface 

 water and thus the amount which is carried oflf is raised to a maximum. 

 A well-limed soil, on the contrary, in which the ])articles are ])erfectly 

 llocculated, is nuu;h more pervious and the amount of water which will 

 be retained and delivered gradually to vegetable growth is much 

 greater. Thus the beneficial effects of lime are manifested in both 

 ways — in the better retention of the flocculated clays and in increas- 

 ing the capacity of the soil for holding a given amount of water in its 

 interstitial spaces. 



There are many other salts which also have the same properties as 

 those of lime, but I have sjjoken of lime salts chiefly because they are 

 cheaper and therefore more economically applied. Perhaps next to 

 lime, common salt would be the most efficient in producing the results 

 already described; but connnon salt being extremely soluble would 



