84 REPORT — 1861. 



in such sort as to make it certain that at 300° or 400° it would vanish altog-ether 

 and be followed by a heating effect, as is observed in hydrogen at low temperatures. 



In diflerent gases the cooling- ettect is very various. It is 5 times as great in 

 carbonic acid as in atmospheric air at low temperatures, and 4 times as gi-eat at 

 the boiling temperature. 



A very remarkable fact which has been elicited by these experiments, is that a 

 gas mixed with another does not exhibit the same thermal effects as it does when 

 tmdiluted. In general a mixtm-e of gases gives a smaller cooling effect than would 

 be deduced from the cooluig effects of the con.stituents. This has been verified in 

 the dilutions of carbonic acid and hydrogen and in atmospheric air, of which each 

 of the component gases has a larger cooling effect than itself 



The authors regret that they have not been able as yet to extend the experiments 

 so as to show the point at which the cooling effect ceases and is followed by a 

 heating effect in the different gases. 



071 some points in connexion tvith the Exhaustion of Soils. 

 By J. B. Lawes, F.R.S., F.O.S., and Dr. J. 11. Gilbert, F.R.S., F.C.S. 



_ The question of the exhaustion of soils was one of peculiar interest at the present 

 time, not only on account of the gi'eat attention now paid to the waste of manuring 

 matters by the discharge of the sewage of towns into our rivers, but also from the 

 fact that Baron Liebig has recently m-ged that om- soils are suffering progressive 

 exhaustion from this cause, and predicted certain, though it may be distant, ruin to 

 the nation, if our present modes of procedure be persevered in. 



The questiftn was one of chemical facts ; and the authors had intended to treat it 

 much more comprehensively than they were able to do on the present occasion. 

 They proposed, by way of illustration, to bring forward one special case of pro- 

 gressive exhaustion, occurring in the course of their o^vn investigations ; and then 

 to contrast the conditions of that result with those of ordinary agriculture. 



They had gro-\vn wheat for eighteen years consecutively on tlie same land, respect- 

 ively without manm'e, with farm-yard manure, and with different constituents of 

 manure, and they had determined the amounts of the different mineral constituents 

 taken off in the crop from the respective plots. Numerous Tables of the results were 

 exhibited. The variations in the composition of the ash of both grain and straw, 

 dependent on variations of season and consequent character of development and 

 maturity, were first pointed out. The general residt was, that, with an unfavour- 

 able season, there was a slight though appreciable decrease iu the percentage of lime 

 and potass, and increase in that of magnesia ; and again, an increase in the percentage 

 of phosphoric acid and of silica; and, especiallyin the case of the straw-ash, a decrease 

 in that of sulphuric acid. Turning to the bearing of the results on the main subject 

 of inquiry, it appeared that when ammonia-salts were used alone, year after year, 

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

 appreciable decline in the amount of phosphoric acid, and that of the straw a con- 

 siderable reduction in the percentage of silica. 



When ammonia-salts alone were used, the aniomit of mineral constituents in the 

 ci'op of a given area of land was veiy much increased — 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 amount of mineral constituents obtained in the 

 crop, that there was when the ammonia-salts and mineral manures were used to- 

 gether, or when farm-yard manm'e was employed. The greatest deficiency indi- 

 cated was in the silica and the phosphoric acid, and next in order came potass and 

 magnesia. The exhaustion here apparent was, howe^-er, not to be wondered at, 

 when it is considered that, in these experiments in which both corn and straw were 

 annually removed without the usual periodical return of farm-yard manure, there 

 had been on the average annually taken from the land by the use of ammonia-salts, 

 about t^^ice as much phosphoric acid, about ti^•e times as much potass, and about 

 twenty-five times as much silica, as would be removed under a system of ordinary- 

 rotation with home manm-ing, and selling only't^orn and meat ; in fact, in sixteen 

 years there had been taken from the land as much phosphoric acid as would require 

 thirty-two years, as much potass as would require eighty-two years, and as much 

 silica as would require 400 yeai-s of such ordinary practice to remove. 



