193 ■ 



the particles are deposited according to size (more exactly, according to the 

 proportion of their surface to their mass). The finest particles remain un- 

 commonly long" in suspension since they are held by the attractive power 

 of the water, which is almost comparable to a chemical solution. The at- 

 traction of gravity for these particles is powerless in opposition to this 

 attraction. After the clay, which has been dissolved in a glass cylinder for 

 the experiment, precipitates from a salt solution, it is noticeable that a layer 

 consisting of close, fine clay particles has formed with a comparatively very 

 clear fluid above it. Because of the presence of sodium chlorid, all fine 

 clay particles are precipitated more as a whole (coagulated, according to 

 Schlosing). "Flocculency" is thus produced. The fall of the somewhat 

 coarser particles among these appears to have been held back, while that of 

 finer ones has been somewhat hastened. It has been assumed that probably the 

 presence of the salt has decreased the attraction between clay and water, 

 since the water then lets the clay fall more completely. On the other hand 

 the attraction of clay to clay must have been increased, and it is therefore 

 more compact. Durham- explains the process by the fact that every bit of 

 the attraction of the water otherwise required entirely for the suspension of 

 the clay is satisfied by the salt of the solution. According to him, sulfuric 

 acid acts like the solution of sodium chlorid, and, according to Mayer, all 

 mineral acids behave in the same way. The same is true of mineral salts 

 even in an excess of fixed alkali or ammonia. 



According to the theories now prevailing, electrolytes act flocculently. 

 i. e. all bodies which in an aqueous solution are partially split up into "Ions." 

 Non-electrolytes have no action. At any rate, an electric current precipi- 

 tates the flakes. It should therefore be assumed that the particles distributed 

 in the water are charged with electricity and the cause of the oscillation may 

 be sought in this electric charge^. 



The chief point, worth considering for all cultivated clay soils, lies in 

 the fact that the nitrates, so far as deposition of the clay is concerned, ap- 

 proximate the chlorates and, on account of the ease with which they are 

 washed away, rapidly cause the packing of the soil. By this is explained the 

 mechanical destruction of soils rich in clay, when repeatedly fertilised ex- 

 clusively zvith nitrates. At first fine crops are obtained but later retrogres- 

 sion takes place. Sodium chloride fertilising used for certain plants has 

 naturally the same destructive effect. 



Behrens* calls attention to the real disadvantage of an excessive use of 

 fertilizing salts. Their osmotic action comes especially under consideration. 

 Because of this osmotic action of the soluble salts in the soil, it is more 

 difficult to supply the water needed by the plant and the plant responds by 

 a suitable modification of its organs. In correspondence with the physiolog- 

 ical lack of moisture, the plant reduces its evaporation by forming fleshier 



1 Biedermann's Centralbl. 1883, Nov., p. 7S6. 

 - Chem. News: cit. "Naturforscher" 1878. p. 112. 



3 Ramann, E., Bodenkunde, 2nd. Ed.. Berlin. .1. Springer, 1905. p. 225. 

 * Behrens, J., Ueber Diing-ungsversuche. .Jahresb. d. Vertreter d. angewandten 

 Botanik, II Jahrg. Berlin, Gebr. Borntrager, 1905, p. 28. 



