CALCAREOUS MANURES-PRACTICE. 99 



that purpose, the oxalic acid will let go any other earth or metal, which 

 it had before held in combination. Let us then observe what would be 

 the effect of the known chemical action of these substances, on their meet- 

 ing in soils. If oxalic acid wei-e produced in any soil, its immediate effect 

 would be to unite with its proper proportion of lime, if enough were in the 

 soil in any combination whatever. If the lime were in such small quantity 

 as to leave an excess of oxalic acid, that excess would seize on the other 

 substances in the soil, in the order of their mutual attractive force ; and 

 one or more of such substances are always present, as magnesia ; or, more 

 certainly, iron and alumina. The soil then would not only contain some 

 proportion of the oxalate of lime, but also the oxalate of either one or more 

 of the other substances named. Let us now suppose gypsum, to be applied to 

 this soil. This substance (sulphate of lime) Is composed of sulphuric acid 

 and lime. It is applied in a finely pulverized state, and in quantities from 

 half a bushel to two bushels the acre— generally not more than one bushel. 

 As soon as the earth is made wet enough for any chemical decomposition 

 to take place, the oxalic acid must let go its base of iron, or alumina, and 

 seize upon and combine with the lime that formed an ingredient of the 

 gypsum. The sulphuric acid left free, will combine with the iron, or the 

 alumina of the soil, forming copperas in the one case, and alum in the 

 other. The gypsum no longer exists— and surely no more satisfactory 

 reason can be given why no effect from it should follow. The decomposi- 

 tion of the gypsum has served to form two or perhaps three other sub- 

 stances. One of them, oxalate of lime, like all salts of lime, is probably valu- 

 able as manure, but the very small quantity that could be formed out of one 

 or even two bushels of gypsum, might have no more visible effect on a whole 

 acre, than that small quantity of calcareous earth, or farm-yard manure. 

 The other substance certainly formed, copperas, is known to be a poison 

 to soil and to plants— and alum, of which the formation would be doubtful, 

 I believe is also hurtful. In such small quantities, however, the poison 

 would be as little perceptible as the manure— and no apparent effect what- 

 ever could follow such an application of gypsum to an acid soil. So small 

 a proportion of oxalic acid, or any oxalate other than of lime, would suffice 

 to decompose and destroy the gypsum, that it would not amount to one 

 part in twenty thousand of the soil. 



Why gypsum sometimes acts as a manure on acid soils, when applied in 

 large quantities for the space, is equally well explained by the same theory. 

 If a handful, or even a spoonful of gypsum is put on a space of six inches 

 square, it would so much exceed in proportion all the oxalic acid that 

 could speedily come in contact with it, that all would not be decomposed, 

 and the part that continued to be gypsum would show its peculiar powers 

 perhaps long enough to improve one crop. But as tillage served to scatter 

 these little collections more equally over the whole space— or even as repeat- 

 ed soaking rains allowed the extension of the attractive powers— applications 

 like these would also be destroyed, after a very short-lived, limited, and 

 rarely profitable action. 



Soils that are naturally calcareous cannot contain oxalic acid combined 

 with any other base than lime. Hence, gypsum applied there continues 

 to be gypsum— and. exerts its great fertilizing power, as in the counties of 

 Loudoun and Frederick. But even on these most suitable soils, this manure 

 is said not to be certain and uniform in its effects, and of course more cer- 

 tain results are not to be looked for with us. T have not umlertaken to ex- 

 plain its occasional failures any more than its general success, on the lands 

 Avhere it is profitably used in p-eneral— but only why it cannot act at all, on 

 lands of a different kind. 



