1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 427 



of water, and digested with frequent shaking for over four 

 months, the green precipitate being then filtered off, dried and 

 analyzed for copper : 



Weight of precipitate taken 100.00 mg. 



Cu found 47.85 



Theoretical Cu in basic carbonate 57.38 



Indicating by the formula above a conversion to basic carbonate 

 of copper of over 83 per cent of the solid carbonate of lime pres- 

 ent. Bicarbonate of lime in solution also reacts with copper 

 sulphate to form the basic carbonate 



CaH, ( CO, ) , + 4 CUSO4.5 H^O = 2 Cu ( OH ) ^.CuCOg + 



CaSO^ + 3 H2SO4 + 16 H,0 

 3 CaH.CCOg), + 3 H,S0, = 3 CaSO, + 6 PLO + 6 CO. 



The silicates of the soil, also, and particularly those of zeolitic 

 character, react readily with soluble copper compounds to form 

 insoluble copper silicates. Organic matter likewise combines 

 with large amounts of copper, to form compounds of indefinite 

 or unknown composition. As a result of all these reactions, when 

 soils are shaken up with solutions of copper salts the latter are 

 withdrawn from solution in large amount. Under irrigation con- 

 ditions, where waters containing minute amounts of copper are 

 filtered through relatively large masses of soil, this action is 

 nearly or quite complete. 



Five large percolators were arranged with varying depths of 



TABLE XVI 

 Percolation of Copper Solutions Through Soils 



Solution used 



Cu compound p.p.m 



Cu ( OH ) s.CuCOa in CO, water 95 

 Cu ( OH ) o.CuCOa in CO^ water 95 

 Cu ( OH ) o.CuCO:, in CO, water 95 

 Cu ( OH ) 2.CUCO3 in COo water 56 



Cu in Amount of Copper in 



solution, percolate, percolate, 

 c.c. p.p.m. 



2000 none 

 1500 none 

 2000 none 

 2000 .85 



Cu ( OH ) ..CuCOa in COo water 8.5 



CuS0,.5 H,0 



254 



600 



150 



7.3 



