CHEMICAL SCIENCE. 227 



The question of the exhaustion of soils is one of peculiar interest 

 at the present time, not only on account of the great attention now 

 paid to the waste of manuring matters discharged into our rivers in 

 the form of town sewage, but also from the fact that Baron Liebig 

 has recently maintained that our soils were suffering progressive ex- 

 haustion from this cause, and predicts certain, though it may be dis- 

 tant, ruin to the nation if our modes of procedure be persevered in. 

 The question was one of chemical facts ; and the authors had it in 

 view to treat it much more comprehensively than they were enabled 

 to do on the present occasion. They proposed, by way of illustra- 

 tion, to bring forward one special case of progressive exhaustion, 

 occurring in the course of their own investigations, and then to con- 

 trast the conditions of that result with those of ordinary agriculture. 

 They had grown wheat for eighteen years consecutively on the same 

 land, both without manure and with different constituents of manure, 

 and they had determined the amounts of the different mineral con- 

 stituents taken off from each plot. Numerous tables of the results 

 were exhibited. The variation in the composition of the ash of both 

 grain and straw, dependent on variation of season, was first pointed 

 out. Reverting to the main subject of inquiry, it appeared that 

 when amnioniacal salts were used alone, year after year, on the same 

 land, the composition of the ash of both grain and straw showed an 

 appreciable decline in the amount of phosphoric acid, and that of the 

 straw a considerable reduction in the" percentage of silica. The av- 

 erage yield of mineral constituents was very much increased by the 

 use of ammoniac al salts, much more so than when a liberal supply of 

 mineral constituents alone was used. But in neither of these cases 

 was there anything like the yield of mineral constituents that was 

 obtained when the amnioniacal salts and mineral manures were used 

 together, or when farm-yard manure was employed. The greatest 

 deficiency indicated was in the silica and the phosphoric acid ; and 

 next in order came potash and magnesia. The exhaustion here ap- 

 parent was, however, not to be wondered at, when it was considered 

 that in these experiments, in which both corn and straw had been 

 annually removed without the usual periodic returns of farm-yard 

 manure, there had been taken from the land, by the use of amnionia- 

 cal salts alone, for sixteen years, as much silica as would require four 

 hundred years, and as much phosphoric acid as would require thirty- 

 two years, and as much potash as would require eighty-two years 

 of ordinary rotation with home manuring, and selling only corn and 

 meat, to remove. Again, in the experiments of the Rev. Mr. 

 Smith, of Lais-Weedon, on the growth of wheat year after year on 

 the same land, the authors estimated that he annually took from 

 each acre about seven times as much potash, about three and a half 

 times as much phosphoric acid, and about thirty-seven times as much 

 silica, as the ordinary course of practice would do ; and yet, after 

 some fifteen years, his crops were said to be not at all failing. The 

 authors did not recommend such practice as that quoted either from 

 their own or Mr. Smith's experiments; but the instances given 

 showed the capabilities of certain soils ; and in one case the condi- 

 tions under which the point of comparative exhaustion had been 

 reached. It was of course impossible to state the limits of the capa- 



