1865.] Agriculture. 261 



from the best chemists of our own country, the practical farmer might 

 very well hesitate to maintain the judgment he had formed. We do 

 not pretend to a discussion here of the elaborate chemical report on 

 this subject, which Baron Liebig has addressed to the Lord Mayor of 

 London. But even the intelligent agriculturist can perceive one or 

 two defects which it exhibits as a specimen of sound reasoning. In 

 the first place, it evidently abandons the true Baconian philosophy in 

 the method by which it professes to determine the composition and 

 the value of the article it discusses. 



The proper way to determine the composition of town sewage 

 clearly is to obtain a fair and average sample of it, and subject it to 

 analysis. Liebig, however, arrives at its value, not by examination, 

 but by reasoning. He considers the food that is consumed in the 

 Metropolis — the waste attendant on the cooking of so large a quan- 

 tity — the average waste of the digestive process in adults and children 

 — the quantity of urine and faeces voided by animals in the streets ; 

 and assuming that a certain proportion of all this will reach the 

 sewers, he concludes what sewage is from what he thus believes it 

 ought to be. This, however, is clearly not the sound or philoso- 

 phical way of determining the point on which the whole of his 

 subsequent reasoning rests. 



Again, the reader of his report can hardly fail to notice a 

 remarkable inconsistency in his valuation of the fertilizing powers 

 of guano and of sewage water respectively. Guano he makes out 

 to be agriculturally worth only 11. 14s. per ton — a conclusion 

 entirely upset by the actual fact, for the agricultural experience 

 of the value ;of guano is large and long enough to make it certain 

 that the market value, 111. or 13Z. per ton, is not more than agricul- 

 turists find it to be their interest to give. But the method by which 

 he reaches so remarkable a result — namely, a discussion of only the 

 ready-made ammonia, along with the phosphoric acid and potash 

 which it contains, does not bind him when he values sewage-water. 

 The urea, with its "potential" ammonia, as Dr. Ure called it, goes 

 for nothing in the case of guano — but is all calculated, in the 7 grains 

 per gallon allowance, at its full ammonia power in sewer water ; and 

 this is an inconsistency which must certainly diminish the influence of 

 the paper published by the Baron on this subject. The practical agri- 

 culturist, moreover, who judges of the conclusion which it indicates, 

 by his experience in the field, will certainly refuse his acquiescence. 

 The ideas which it teaches, that the agricultural value of a manure can 

 be determined anyhow but in the field — that the material put into the 

 land in dung will all reappear in the consequent increase of the crop 

 — that arable cultivation offers the best circumstances for the full 

 realization of the fertilizing power of sewage, are all utterly opposed 

 to the experience of the farmer. And, of course, the experience of the 

 farmer must, after all, be conclusive on this subject. Once get the 

 agricultural verdict, and it must be final — it is necessarily the true 

 one. Whatever may be the prepossessions of the man of science 

 there can be no appeal. Hence it is, that if we can show how the 

 analogy of agricultural experience bears upon the sewage question, 

 and, still better, it we can quote the records of actual agricultural ex- 



