TRANSACTIONS OF THE SECTIONS. 85 



Again, the authors estimated that in tlie experiments of the Eev. Mr. Smith of 

 Lois Weedon, on the growth of wheat j^ear after j-ear on the same land, -nathout 

 manure, there had been an annual extraction from eacli acre of land of about three 

 and a half times as nuich phosphoric acid, about se-\-en times as much potass, and 

 about tliirty-scven times as nuicli silica, as tliere would be in the ordinary course 

 of practice ; yet, after some fifteen years tire crops at Lois Weedon were said not 

 to be at all failing. 



The authors did not recommend such exhaustive practice as that quoted from 

 their O'wn, or the Rev. Mr. Smith's experiments. But the instances given showed 

 the capabilities of certain soils ; and in one case the conditions under which the 

 point of comparative exhaustion had been reached. It was, of com'se, impossible to 

 state the limits of the capability of soils generally, so infinitely varied was their 

 composition ; but it would be useful to give an illustration on this point. Reckon- 

 ing the soil to be one foot deep, it was estimated that it would require, of ordi- 

 nary rotation with home manuring and selling only corn and meat, about 1000 

 years to exhaust as much phosphoric acid, about 2000 years to exhaust as much 

 potass, and about 6000 years to exhaust as much silica, as, according to the average 

 results of forty-two analyses* relating to fourteen soDs of very various descriptions, 

 had been found to be soluble in dilute hycbochloric acid. Many soils had, doubt- 

 less, a composition inferior to that here supposed. In a large proportion, however, 

 the amounts of the above constituents assumed to be soluble in dilute hydrochloric 

 acid woidd probably be available for plants long before the expiration of the periods 

 mentioned ; whilst, in a large proportion, there would still be further stores even- 

 tually available within a greater or a less depth from the surface. 



But the exhaustion of mineral constituents by the sale of com and meat alone 

 was in reality not so gi-eat, in the ordinary practice of this country, as has been 

 assimied for the piu^ose of the above illustrations. Wliere there was no purchase 

 of cattle-food, or of artificial or town manm'es, the sales of com and meat woidd on 

 the average be much less than were taken in the authors' estimates ; and where such 

 materials were purcha.sed with any degTCe of j udgment in the selection, there would 

 always be much more phosphoric acid (othei-wise the most easily exhausted con- 

 stituent) so brought upon the land, than woidd be obtained from it in the increase 

 of produce yielded ; in fact, under such conditions, in many soils potass was more 

 likely to become deficient. Again, by no means the whole of the mineral consti- 

 tuents sent from the farm in the form of corn and meat will reach the sewers of 

 our towns, and thence our rivers ; a not inconsiderable portion finding its way back 

 to the land in some fomi ; in addition to which, imported com, meat, and other 

 materials will contribute something to the restoration of our own cidtivated land. 

 It is at the same time certain that so much of the refuse matters of oiu* towns as 

 becomes diluted with water in the degTeo recognized under the present sewerage 

 system will be applicable as manure, on the large scale, only to succulent crops, and 

 especially to grass-land ; and, so far as this is the case, they will of com'se not 

 directly conti-ibute to the restoration to the land imder tillage, of the mineral con- 

 stituents sent from it in its produce of corn and meat. When other descriptions of 

 produce than com and meat, such as roots, hay, or straw, .are largely sold, compen- 

 sation is generally made by the return to the hand of stable- or town-manures of 

 some kind. If this be not done, the loss of mineral constituents may indeed be 

 very considerable. 



In conclusion, whilst the authors insisted upon the importance of applying to 

 agiicultm-al purposes as much as possible of the valuable manuring matters of our 

 towns, they at the same time believed that modem practices, taken as a whole, did 

 not tend to exhaustion in anything like the degree that had been supposed by some. 



On Purifying Towns from Sewage hy means of Dry Cloacce. 

 By Dr. J. H. Llotb. 



On the Proportion of Tin present in Tea-Lead. By Dr. S. Macadam. 



* The accuracy of some of these analyses, however, is admitted as open to question : 

 see Report by Magnus, Ann. d. Landwirthschaft, xiv. 2. 



