Effects of Soil upon Toxicity 



177 



soil resting on filter paper supported by a perforated porcelain 

 plate. Two soils, heavy clay and sandy loam, were employed; 

 and two copper solutions, sulphate and bicarbonate. 



In nearly all cases copper as basic carbonate was entirely 

 removed from solution in percolating through as little as a 

 single inch of sandy loam. Although appreciable amounts of 

 copper sulphate passed out of a soil, the latter in that case itself 

 contained a very small percentage of copper. Inasmuch as 

 soluble copper in irrigating waters must be present ordinarily 

 as basic carbonate, its complete withdrawal by thin layers of soil 

 is significant in connection with irrigated crops. 



Irrigation Experiments 

 A set of cultures was arranged to test the effects upon crop 

 plants of solutions of basic copper carbonate so applied as to 

 filter through the soil before reaching the plant roots. Six-inch 



Fig. 5. — Diagram of pot culture irrigated through two-inch pot inside. 



flower-pots were filled with sandy loam soil. In the middle of 

 each of these pots a two-inch pot was half buried, and the plants 

 experimented with were grown in the circles of soil between the 

 large and small pots. These plants were irrigated by pouring 

 the solution used into the small pot, through the bottom of which 

 it passed, necessarily filtering through more or less soil before 



