J. J. Griffith 385 



Lime Eequirements. 



There appears to be a consensus of opinion among farmers that 

 manuring affected land does not lead to any improvement. Several 

 cases have been observed where a dressing of dung supplemented by 

 artificials including nitrate, phosphate and potash, effected practically 

 no increase in crop production. With reference to the efficacy or other- 

 wi.se of liming, however, there seems to be no general agreement. Con- 

 sequently, it was considered advisable to ascertain the lime require- 

 ments of mine refuse and also that of contaminated and uncontaminated 

 soils. Some of the results are given in Table IX. 



Table IX. Lime Requirements in tons per acre. 



Sediment Cwm Merfin leat 1^95 



Except in a few cases, more particularly the neighbourhood of such 

 mines as Level Fawr and Frongoch which contain considerable quan- 

 tities of pyrites or marcasite, contamination does not increase the lime 

 requirements of soils very materially. For further reference to this 

 matter see Pot Experiments, Table XX, and Field Experiments. 



The form in which lead occurs in the soil. 



Lead is carried on to the land mainly in the form of galena, and it is 

 found that sulphuretted hydrogen is evolved from all recently con- 

 taminated soils when they are digested with strong hydrochloric acid. 

 Affected soils which have not been contaminated recently are found to be 

 free, or nearly free, from sulphides. So, in course of time lead sulphide, 

 in the soil, is changed into some other compound or compounds of lead. 

 In the mines, under the influence of water-containing carbonic acid, 

 galena is changed to cerussite. Consequently, one would expect the lead 

 sulphide in the soil to be converted to lead carbonate. 



