54 SOURCE AND ASSIMILATION OF NITROGEN. 



The carbonate of ammonia contained in rain-water is decomposed 

 by gypsum, in precisely the same manner as in the manufacture 

 of sal ammoniac. Soluble sulphate of ammonia and carbonate 

 of lime are formed ; and this salt of ammonia, possessing no 

 volatility, is consequently retained in the soil. All the gypsum 

 gradually disappears, but its action upon the carbonate of ammo- 

 nia continues as long as a trace of it exists.* 



The beneficial influence of gypsum and of many other salts 

 has been compared to that of aromatics, which increase the 

 activity of the human stomach and intestines, and give a tone 

 to the whole system. But plants do not contain nerves : we 

 know of no substance capable of exciting them to intoxication 

 and madness, or of lulling them to sleep and repose. No sub- 

 stance can possibly cause their leaves to appropriate a greater 

 quantity of carbon from the atmosphere, when the other constitu- 

 ents required for the growth of the seeds, roots, and leaves, are 

 wanting."]" The favorable action of small quantities of aromatics 

 upon man, when mixed with his food, is undeniable ; but aro- 

 matics are given to plants without food to be digested, and still 

 they flourish with greater luxuriance. 



It is quite evident, therefore, that the common view concerning 

 the influence of certain salts upon the growth of plants evinces 

 only ignorance of its cause. 



The action of gypsum, chloride of calcium, and of other salts 

 of lime, really consists in their giving a fixed condition to the 

 nitrogen, or ammonia, introduced to the soil. This nitrogen is 

 indispensable for the nutrition of plants. 



In order to form a conception of the effect of gypsum, it may 

 be sufficient to remark that 100 lbs. of burned gypsum fixes as 



* It has long been the practice in some parts of the country to strew 

 the floors of stables with gypsum. This prevents the disagreeable odor 

 arising from the putrefaction of stable manure, by decomposing and re- 

 taining the ammoniacal salts. — Ed. 



" I lixiviated some earth," says Spatzier, " and in the filtered solution, 

 after evaporation, I obtained an appreciable quantity of sulphate of ammo- 

 nia." — ErdmarCs Journal, 1831, Bd II , s. 89. 



f Schubler states that white arsenic in small quantity exerts a beneficial 

 action upon vegetation — a fact proved by Lampadius, who manured whole 

 fields with this substance. 



