1917] Lipman-Gericlce : Smelter Wastes and Barley Growth 553 



the conditions here discussed. Since it is rare in nature that 

 more than the lowest concentrations of copper and zinc here 

 studied ever occur in soils suited to crop production, the ques- 

 tion of the danger in the use by man and animals of plants 

 absorbing copper is not a serious one, for with small quantities 

 of copper and zinc present in the soil, very small quantities only 

 are absorbed by the plant. It must be added here, morever, that 

 we employed easily water-soluble salts, whereas in nature the 

 compounds of the metals found are principally those of a very 

 insoluble nature. The latter circumstance would perforce make 

 impossible any large concentration of any metal in the soil solu- 

 tion, and hence only small quantities could be absorbed by plants. 



We were interested also in obtaining an inkling as to the 

 fate of the copper and zinc added to the soil after three seasons 

 of plant growth thereon. Accordingly', several soils were chosen 

 for examination. Pots receiving 600, 1800, 2000, and 3000 p. p. 

 m. CuSO^ gave the following results : In the first case all the 

 copper added was recovered. In the second case 1750 p. p. m., 

 instead of 1800, were recovered. In the third case all the cop- 

 per was recovered, and in the fourth case 2875 p. p. m. were 

 recovered, instead of 3000 p. p. m. 



In the case of zinc the pots receiving 800, 1700, and 2000 

 p. p. m. ZnSO^ were studied. In the first case 750 p. p. m. were 

 recovered. In the second case 1650 p. p. m. were recovered in 

 one soil, and 1500 p. p. m. in another soil. In the third case only 

 1250 p. p. m. were recovered. 



These data indicate that in the case of copper, at least, the 

 soil clings tenaciously to the metal ; and most of it, or nearly all 

 of it, can be recovered from the soil even three seasons after it 

 has been incorporated therewith, and three crops of barley 

 grown in the interim. With zinc, there do appear to be losses. 

 These may perhaps be explained in part by the larger amounts 

 of zinc than copper absorbed by plants, and by the lesser accu- 

 racy of the method for its determination as compared with that 

 employed for copper. Twenty-gram samples of soil were em- 

 ployed in all cases for obtaining the extracts which were an- 

 alyzed, and it is therefore believed that the error involved in 

 the analyses could not have been very large. 



