366 TRANSACTIONS OF THE 



place in those countries at long intervals, say of 21 years, and it was a pro- 

 verb in respect to calcareous marls, that no farmer ever lived to see his 

 field marled a second time. The quantity of slaked lime applied at such 

 intervals, in Scotland, was, according to Sir John Sinclair, as much as 600 

 bushels per acre, to stiff clay, and 200 bushels per acre to sand. In other 

 cases, however, it was well known that the application of far less c^uanti- 

 ties rendered soils barren for several years. Chemical .investigation has 

 shosvn that where such was the case, the limestone contained the cabonate 

 of magnesia, as well as that of lime. Such a limestone does not fall to 

 powder on the effusion of water, but although broken by it into lumps, 

 may, if buried in the ground, remain caustic for months, destroying the 

 organic matter which may come in contact with it. The magnesia also 

 does not appear to enter, except in exceedingly minute quantities, into the 

 constitution of plants, and if absorbed, affects their vitality. Now, all the 

 limestones in the region in Pennsylvania in which lime is so advantageously 

 used, are magnesium, and experience has limited the application of the 

 lime obtained from them to 20 or 30 bushels per acre. 



Except in the case of reclaiming the lands which yield peat or turf, such 

 as the mosses of Scotland and the bogs of Ireland, where 200 or 300 

 bushels of caustic lime per acre have been found beneficial, large quanti- 

 ties, even of a pure slaked lime, are unnecessary. In some portions of 

 France, distant from quarries of limestone, and where fuel is scarce, ne- 

 cessity has taught the most economic use of lizue. This consists in form- 

 ing it into compost with sods and refuse vegetable matter. The heaps are 

 frequently turned by the plow, and when the incorporation is complete, are 

 carted out and spread upon the ground. In this way it is said that seven 

 bushela per acre are ample, but the application must be repeated in advance 

 of every wheat crop. 



In continuation, he stated that the carbonate of lime, except in small 

 quantities, did not enter into the constitution of any plants, and was not a 

 proper food for many of them. It therefore vras not a numure, in the 

 farmer's sense of the word, except for the cereal gramina, to which it also 

 yielded the base of the phosphate of lime, which seemed essential to the 

 filling of the ears. The carbonate of lime, however, permitted larger quan- 

 tities of putrescent manures to be applied to the soils which contain it,- 

 naturally or applied, and prolonged their eff"ect by retaining the gases gen- 

 erated by their decomposition. 



He, in conclusion, said that the subject would not be complete, did he 

 not say something in reference to the use of sulphate of lime, gypsiim, or 

 as more familiarly known, plaster. He had already referred to the mode 

 of preparing it for the use of the agriculturist b}' mechanical crushing, and 

 not by heat. This statement set at naught the explanation of its action 

 given by some, namely, that the plaster absorbed moisture from the air, and 

 gave it out slowly to the plants. The true theory of the use of plaster is 

 the same as that of the 4th reason assigned by him for the use of lime, 

 namely, that it is an essential constituent of some plants. Thus it has 



