246 Journal of Agricultural Research voi. xix, no. 6 



Attention is called to the fact that, although both greensands showed 

 a high lime requirement when tested by the Veitch method, neither of 

 them gave evidence of more than a trace of acidity in the water extract. 

 The addition of sulphur to the greensand in the proportion of 3 parts green- 

 sand to I part sulphur caused a gradual accumulation of water-soluble 

 acidity, because of the slow oxidation of the sulphur. Composts 3 and 10, 

 in which both sulphur and manure were mixed with the greensand, show 

 a slight and gradual accumulation of water-soluble acidity up to the end 

 of the fifth week, after which there is a very rapid rise for three weeks. 

 For the remainder of the period the acidity fluctuates at a high and 

 practically constant level. When one-half of the manure is replaced 

 by an equal quantity of soil, as in composts 4 and 1 1 , the acidity is greatly 

 reduced, the maximum for the Maryland greensand being reached at 

 the end of the 12-week period and for the New Jersey greensand after 

 15 weeks. When the manure was entirely replaced by soil, the acidity 

 increased gradually throughout the entire period, as shown by composts 

 5 and 1 2 ; but the amount developed was only about one-third as much 

 as when equal weights of soil and manure were used. This indicates 

 rather strongly that in composts made up with a greensand deficient in 

 calcium carbonate the rate of development and the amount of acidity 

 depend very largely on the amount of organic matter present. A 

 further comparison of composts 5 and 12 with 2 and 9 seems to sub- 

 stantiate this conclusion, in that the soil used contained a small amount 

 of organic matter. 



The acidity titrated did not, of course, at any time consist entirely of 

 free sulphuric acid. As sulphofication progressed and the amounts of 

 free sulphuric acid and sulphates increased, an increasing amount of acid 

 silicates was obtained in the water extract and was precipitated upon 

 titration with the alkali. Careful inspection of several titrations, made 

 after the maximum acidity had been attained, seemed to indicate that 

 from 45 to 55 per cent of the acidity titrated was due to free sulphuric 

 acid, the remainder of the acidity being due to acid silicates and other 

 acid salts. 



Under the conditions of our experiment the addition of ferrous sulphate 

 and aluminum sulphate when used at the rate recommended by McLean 

 (ii) for sulphur-floats composts has had no appreciable effect, as may be 

 seen by a comparison of composts 6 and 13 with 5 and 12. The addition 

 of ID gm. of calcium carbonate to the sulphur-manure-soil compost had 

 a marked stimulating effect, beginning about the third week in the New 

 Jersey greensand compost and two weeks later in the Maryland greensand 

 compost. In the former the stimulating action persisted up to the end of 

 the experiment, while in the latter the effect of the calcium carbonate had 

 entirely disappeared at the end of 1 2 weeks. A cause for this difference 

 is found when the lime requirement of the New Jersey greensand is 



