74 



Journal of Agricultural Research 



Vol. XV, No. 9 



we are faced with the apparent fact that the potash of the clay is much 

 less soluble, in proportion to the quantity directly exposed to the solvent, 

 than that of the nonclay. This would tend to negative, at least for 

 these two soils, the widely held theory that the soil particles are covered 

 with a fairly homogeneous celloid coating from which weak solvents take 

 up most of the materials they gain from the soil in a short time after 

 they begin to act upon it; or else, it must be assumed that such coatings 

 are much thicker on the nonclay than on the clay particles. 



It is here needful, however, to qualify our acceptance of these con- 

 ventional estimates of the surface areas of the particles acted upon. 



It was noted in an earlier paragraph, that the larger proportion of the 

 clay particles, when their watery suspensions were examined micro- 

 scopically, showed diameters less than 0.0025 mm., the mean diameter 

 for the clay group. The effect of the average diameter being in these 

 cases less than the mean diameter for the clay group is, of course, to 

 increase, possibly in quite large degree, the corresponding surface areas 

 and to diminish correspondingly the quantity of potash dissolved from 

 a unit area. 



On the other hand, the portions of the washed clays and nonclays 

 submitted to solvent action had been air-dried after separation by sedi- 

 mentation. A portion of each of the air-dried clays was shaken up with 

 water to see whether the drying had resulted in any flocculation or cement- 

 ing of the particles. It was found difficult to get all the clay back into 

 suspension, even with the aid of a little ammonia added to deflocculate. 

 Still, the proportion of the dry clay not readily taken back into suspension 

 was relatively small. Another condition, possibly much more highly 

 determining in its effect, is found in the fact that ammonium-chlorid 

 solution itself acts as a flocculant, so that a free exposure of the surfaces 

 of the clay particles is impossible in its presence. 



POTASH IN CROPS HARVESTED FROM THE UNTREATED AND POTASH- 



DRESSED LANDS 



No Studies of the potash content of the crops from plots i and 4 of 

 Tier II were made in connection with the present investigations. There 

 are available, however, two sets of analyses made of crops harvested at 

 different times from the plots of corresponding numbers and history 



