290 ACTIONS OF ARTIFICIAL MANURES 



we may calculate an average figure of 117 Ib. of carbonate 

 of lime removed from each 200 Ib. of ammonium - salt 

 applied. This figure would indicate that the carbonate of 

 lime removed is the chemical equivalent of the ammonium- 

 salts supplied as manure, which suggests that when they 

 reach the soil they begin by reacting with the carbonate of 

 lime, and not with the zeolites as originally suggested by 

 Way. However, direct experiments made to test this point 

 (Hall and Gimingham, Trans. Chem. Soc., 91 (1907), 677) 

 showed that though some interaction will take place between 

 the ammonium - salts in solution and carbonate of lime, the 

 zeolites bring about by far the greater part of the change, 

 even when the carbonate of lime constitutes as much as 

 20 per cent, of the soil. Probably the carbonate of lime is 

 brought into the action later, when the ammonia is liberated 

 from its zeolitic compound in order to be converted into 

 nitrate or taken up directly by the plant ; the question is 

 in any case only of technical interest, since there is no doubt 

 about the final result that the ammonium sulphate behaves 

 like an acid, and removes from the soil whatever amount of 

 carbonate of lime is required to combine with the sulphuric 

 acid it contains. 



So far the matter of the wastage of carbonate of lime is 

 clear enough ; but another problem was set up when Dr J. A. 

 Voelcker observed that the soil of the permanent wheat and 

 barley crops at Woburn, which had been receiving ammonium 

 salts for about twenty years, had become actually acid to 

 litmus paper (see Jour. Roy. Ag. Soc., 60 (1899), 515, and 

 62 (1901), 286). The acidity thus developed rendered the land 

 unable to carry barley, though its capacity to do so was 

 restored by a comparatively small dressing of two tons of 

 lime to the acre. Naturally acid soils had been known 

 before, chiefly in peaty water-logged areas, but this was the 

 first example recorded of a soil becoming acid through a par- 

 ticular course of treatment. That the acidity had developed 

 upon the Woburn plots and not at Rothamsted, where the 



