70 



I. The Hills' Experiments. 



These — if I may be allowed still to apply the term to them — 

 embraced in 1922 : — 



(i\) The action of (X)mpoiinds of Lead on wheat. 

 (/)) The action of Chroiniiim (•()m|)()iincls on wheat. 



[a) Lhad Compounds. 



In previous work in li)12 (journal R.A.S.E., 1912, pp. 32-1-5) 

 it was found that lead salts, when present to the extent of .03% 

 of lead in the soil, exerted no harmful influence in the case of the 

 phosphate, nitrate or <\'irbonate. In 191-1 (Journal R.A.S.E., 

 1914, pp. 312-3) the same salts, but in higher amount (up to .10% 

 of lead), and with the sulphate and chloride additionally tried, 

 similarly failed to show any injurious effect. The subject was then 

 left for a time, but I returned to it now, taking- still higher 

 amounts of the metal and using- the following compounds of lead, 

 the oxide (litharge), carbonate, sulphate and chloride. The quan- 

 tities now employed were respectively .25%, .50% and 1% of the 

 metal. The salts were mixed with the whole of the soil in each 

 pot, and each experiment was, as usual, in duplicate, the soil being 

 that from Stackyard Field. 



Wheat was sown on December 20th, 1921, and nothing was 

 noticeable with regard to germination except in the case of the 

 lead chloride sets. In these .25% slightly retarded germination, 

 .50% still more so, and 1% very markedly. The full number of 

 plants did not come up in any of these. 



The only differences between the crops, and only signs of any 

 toxic influence were with the chloride; with this, .25% did not 

 appear to do any harm, but with .50% there were only one or tw^o 

 weakly plants left, while with 1% the few plants that came up at 

 first died away entirely. 



Plate I. shows the appearances very clearly, and the compara- 

 tive weights In the case of the chloride are given below. 



Lead Chloride upon Wheat, 1922. 



From this experiment it would result that lead present as 

 chloride in a soil will produce a toxic effect as soon as the quantity 

 exceeds .25% of lead, but that in the forms of the oxide, carbonate 

 and sulphate, no harmful influence is exercised up to 1% of lead. 



(b) Chromium Compounds on Whkat. 



1. — The experiments of 1920 and 1921 with chromate and bi- 

 chromate of potash were continued for a third year, the sanie pots 

 without alteration or addition being used again for a third corn 

 crop which was sown on October 27th, li)21. 



By way of recapitulation, it may be said that in the first year 



