460 GYPSEOUS EARTH. 



decomposable fertilizing ingredients. As the applications had not 

 been made with any view to this question, the experiments are not 

 to be deemed as conclusive, and the correctness of this inference is 

 yet to be fairly tested by future experiments.* But the benefits 

 from some of the dressings, and all of those supposed to be from 

 the deeper digging, were so great, and so speedily produced, that 

 renewed and strong interest was excited in regard to this manure. 

 The quantity applied was generally 40 bushels of the earth to the 

 acre. And this quantity seemed (from an accurate comparative 

 experiment) to produce as much benefit as 200 bushels. The 

 growth of clover was increased in degrees varying from 100 to 300 

 per cent. And where the application was most successful, the in- 

 crease and profit were sufficient to compensate the expense, even 

 though no further benefit shall be found than in this one crop or 

 that a new application shall be required, and be made, for every 

 succeeding crop of clover, or once in each round of the rotation of 

 crops. 



An observation made by accident last spring led to further 

 chemical as well as other examinations of this earth, and to im- 

 portant results. Upon heating a lump of it to red heat, I found 

 that strong fumes were thereby extricated, which were almost suf- 

 focating if inhaled incautiously. The odour was manifestly sul- 

 phureous in part, and principally ; but it seemed not altogether so, 

 but to be mixed with some other, much like that of muriatic acid 

 gas. Similar trials were made on many specimens, and all the 

 darker and (as supposed) richer layers of the green earth at Cog- 

 gins Point showed the like result. From specimens of the upper 

 and lighter green stratum (C r ) when heated red, there was nothing 

 of this suffocating odour produced. And it may be useful to state 

 here, in anticipation of subjects to be hereafter more fully consi- 

 dered, that I subsequently found that the New Jersey green-sand 

 earths yielded not a particle of this gaseous product. 



This odour, so far as it was sulphureous, was obviously the pro- 

 duct of the decomposition (by red heat) of sulphuret [or bi-sulphu- 

 ret] of iron which was thus proved. to be universally diffused, 

 though invisible, through all the darker and better kinds of this 

 earth. Sulphur would have shown like results, with a much less 

 degree of heat ; but it could not be that, because the heat sufficient 

 to decompose sulphur (and to evolve its fumes) had no such effect 

 on the earth. I also observed that lumps of the earth, after having 

 been applied as manure, and exposed on the surface of the ground 

 for some months, often had a smell of sulphur; and, in some cases, 



* Subsequent experiments have not sustained the above idea. But the 

 results, though not uniform, have been so generally beneficial on clover, 

 that this earth is applied to from 60 to 80 acres every year. 



