Rothamsted Symposium on Trace Elements 



92 



were used: copper pyrite (chalcopyrite), bornite with an admix- 

 ture of copper glance (chalcocite), red copper (cuprite) and 

 malachite (see Table 17). 



Field experiments with one of the minerals (chalcopyrite) 

 have been made for several years now in Jutland with good re- 

 sults as compared with copper sulphate. 



If the copper minerals are compared on the basis of the same 

 degree of fineness per unit of weight, malachite and bornite with 

 an admixture of copper glance, with respect to fertilizing value, 

 are nearly alike and nearly equal copper sulphate in their fertiliz- 

 ing effect. Chalcopyrite must be ground very fine if its effect 

 has to reach that of malachite and bornite-copper glance. 



Table 18: — 



Copper pyrite I 



Bornite II 



Bornite I 



Malachite I 



Malachite II 



0,56 

 2,79 

 0,52 

 2,59 

 0,52 

 2,58 



0,47 

 2,34 

 2,50 



0,067 

 0,333 



0,001 1 

 0,003/ 

 0,014 

 0,069 



0,051 

 0,258 



0,004 



20 



59 



62 



50 

 51 



Assuming that the area of the active "copper surface" for the 

 different copper minerals is proportional to the percentage by 

 weight of copper in the mineral it is found that the curves showing 

 the increases in yield for the different minerals fall together as 

 shown in Figure 15, and Table 18. At any rate the deviations 

 have not been really great in these investigations.* Of course 

 it is not to be expected that the surface tension, the solubility of 

 the different minerals at the same relative copper surface is quite 

 the same because the crystallographic structure may be of some 

 importance. Moreover an occlusion of the copper is possible if 

 the copper mineral contains rather large amounts of other minerals 

 as impurities as did copper pyrite. 



According to the results of these investigations the main reason 



• The considerable excess of copper compounds of hydrolysis, left over in the soil, in increasing 

 amounts, from year to year, may well contribute to thii result. 



