96 CALCAREOUS MANURES-PRACTICE. 



experiments,) had both been tried with gypsum, and at different rates of 

 thickness, before marling, without the least effect. Several years after 

 both had been marled, gypseous earth (from the bed referred to, page 93,) 

 was spread at twenty bushels the acre, (which gave four bushels of 

 pure gypsum,) on clover, and produced in some parts a growth I have 

 never seen surpassed. It is proper to state that such 'results have been 

 produced only by heavy dressings. Mr. Thomas Cocke, of Tarbay, 

 in the spring of 1831 sowed nearly four tons of Nova Scotia gypsum on 

 clover on marled land, the field being a continuation of the same ridge 

 that my 1st, 2d, 3d, and 4th experiments were made on, and very similar 

 soil. His dressing, at a bushel to the acre, before the summer had passed, 

 produced evident benefit, where it is absolutely certain, from abundant 

 previous experience, that none could have been obtained before mai'ling. 



On soils naturally calcareous, I have in some experiments greatly pro- 

 moted the growth of corn by gypsum, and have doubled the growth of 

 clover on my best land of that kind. When the marl containing gypsum 

 was applied, benefit from that ingredient was almost certain to be obtained. 



All these facts, if presented alone, would seem to prove clearly the cor- 

 rectness of the opinion, that the acidity of most of our soils caused the 

 inefficacy of gypsum, and that the application of calcareous earth, which will 

 remove the acid, will also serve to bring gypsum into useful operation. But 

 this most desirable conclusion is opposed by the results of other experi- 

 ments, Which, though fewer in number, are as strong as any of the facts 

 that favor that conclusion. If the subject were properly investigated, those 

 facts, apparently in opposition, might be explained so as no longer to con- 

 tradict this opinion, or perhaps might help to confirm it. Good reasons, de- 

 duced from established chemical truths, may be offered to explain why the 

 acidity of our soils should prevent the operation of gypsum; though it 

 may be deemed premature to attempt the explanation of any supposed fact, 

 before every doubt of the existence of the fact itself has been first removed. 



One of the circumstances will be mentioned, which appears at first glance 

 most strongly opposed to the opinion which has been advanced. On the 

 poor acid clay soil, of such peculiar and base qualities, which forms the 

 subject of the 5th, 6th, and 7th experiments, gypsum has been sufficiently 

 tried, and has not produced the least benefit, either before marling, or after- 

 waitis. Yet the first growth of clover on this land afler marling is fully 

 equal to what might be expected from the best operation of gypsum. Now 

 if it could be ascertained that a very small proportion of either sulphuric 

 add, or of the sulphate of iron, exists in this soil, it would completely ex- 

 plain away this opposing fact, and even make it the strongest support of 

 my position. The sulphate of iron has sometimes been found in arable 

 soil,* and sulphuric acid has been detected in certain clays.f I have seen, 

 on the same farm, a bed of clay of very similar appearance to this soil, 

 which certainly had once contained one of these substances, as was proved 

 by the formation of crystallized sulphate of lime, where the clay came in 

 contact with a bed of marl. The sulphate of lime was found in the 

 sinall fissures of the clay, extending sometimes one or two feet in perpen- 

 dicular height from the calcareous earth below. Precisely the same chemi- 

 cal change would take place in a soil containing sulpluuic acid, or sulphate 

 of iron, as soon as marl is applied. The sulphuric acid, (whether free 

 or combined with iron) would immediately unite with the lime presented, 

 and form gypsum, (sulphate of lime.) Proportions of these substances, too 

 small perhaps to be detected by analysis, would be sufficient to form three 



* Agr. Chem. p 141. f Kirwan on Manures. 



