TTtK AMMONIA OF 'tU\t SOtt, ^45 



crystalline solid. Double decomposition lias taken place 

 between the two salts under the influence of water. If, 

 again, the carbonate of lime on the filter be reunited to 

 the liquid filtrate and the whole be evaporated, it will be 

 found that when the water has so far passed off" that a 

 moist, pasty mass remains, the odor of ammonia becomes 

 evident again — carbonate of ammonia, in fact, escaping by 

 volatilization, while sulphate of lime is reproduced. It is 

 a general law in chemistry that wlien a number of acids 

 and bases are together, those which under the circum- 

 stances can produce by their union a volatile body will 

 ixnite, and those which under the circumstances can form a 

 solid body will unite. When carbonic and sulphuric acids, 

 lime and ammonia, are in mixture, it is the circu instances 

 which determine in what mode tliese bodies combine. In 

 presence of nmch water carbonate of lime is formed be- 

 cause of its insolubility, water not being able to destroy 

 its solidity, and sulphate of ammonia necessarily results 

 by the union of the other two substances. When the wa- 

 ter is removed by evaporation, all the possible compounds 

 between carbonic and sulphuric acids, lime and am- 

 monia, become solid ; the compound of ammonia and car- 

 bonic acid being then vohitile, this fact determines its 

 formation, and, as it escapes, the lime and sulphuric acid 

 can but remain in combination. 



To apply these principles : When carbonate of ammo- 

 nia is brought into the soil by rain, or otherwise, it tends 

 in presence of much water to enter into insoluble combi- 

 nations so far as is possible. When the soil becomes dry, 

 these compounds begin to undergo decomposition, provid- 

 ed carbonates of lime, magnesia, potash, and soda, are 

 present to transpose with them ; these bases taking the 

 place of the ammonia, while the carbonic acid they were 

 united with, forms with the latter a volatile compound. 

 In this way, then, all soils, for it is probable that no soil 

 exists which is destitute of carbonates, may give ofi'at th© 



