Action of the Atmospkere upon newly-deepened Soil. 453 



like varieties of trap rock, it will be remembered, was lomid by 

 Leslie, when reduced to a state of mould, to stand next to gar- 

 den-mould in its power of absorbins^ moisture. Oxide of iron, 

 which occurs in large quantities in these minerals, has been 

 found bv all investigfations to have a grreat attraction for am- 

 monia. 



If, therefore, the earth contains much humus, alumina or clay, 

 oxide of iron, or magnesia, in a state of fine division, its power 

 of absorbing gaseous matters from the air will probably be good. 



Rose has also observed that some sulphates possess the pro- 

 perty of absorbing ammonia and of forming with it definite com- 

 pounds, which, unlike the sulphates of ammonia prepared in the 

 moist way, contain no water of crystallization, and easily give 

 out again the ammonia contained in them. They are formed by 

 placing the anhydrous sulphate in a glass tube, and transmitting 

 over it at common temperatures ammoniacal gas, well dried by 

 fused potassa, as long as any increase of weight is observed ; 

 some sulphates absorb the gas very rapidly at first, and with dis- 

 engagement of heat, but the absorption afterwards becomes slow, 

 and requires a day or two to be complete. The salts most re- 

 markable for this property are those which in solution are dis- 

 posed to unite with ammonia. This, it will be observed, is 

 quite a different property from the mere condensation of the gas 

 within a porous body ; here there would appear to be some 

 chemical action. 



Rose compares these compounds to hydrates : water acts as a 

 feeble base to saline compounds, combining with some in one or 

 more proportions, and not at all with others, differing greatly in 

 the ratio in which it combines with different salts, and l)eing 

 abandoned with great facility. The same features characterize 

 the combination of ammonia with the anhydrous sulphates. 

 (P0/7. Amialeii, xx. 149.) 



Rose also found that sulphates are not the only salts Avhich 

 absorlj ammonia ; some nitrates also possess that property, and 

 the nitrate of the oxide of silver absorbs it with such rapidity, 

 and the corresponding increase of temperature is so great, that the 

 salt enters into fusion. 



Relating as this paper does to the action of the atmosphere, 

 the power of soils to combine with and remove substances from 

 solution seems less connected with its object ;* and as Professor 

 Way has so fully treated the matter in recent numbers of the 

 Journal, there is less occasion for here touching upon it. 

 Some of the results arrived at may, however, be alluded to. 

 " Soils were found to possess," says Way, " in a greater or less 



* This remarkable property was observed by Mr. H. S. Thompson in 1845 ; and 

 the subject lias since Ijccu perseverinizly followed by Mr. Way. 



