220 GEOLOGY AND CHEMISTRY OF SOILS. 



catalytic power, and causes the salts and silicates to form 

 themselves into new compounds. Life imparts activity to all 

 the chemical agents. It lets loose the bases of the salts upon 

 the vegetable matter, and they convert it into geine. The 

 liberated acids act upon the silicates and form new salts, 

 ready to be decomposed by the vital power, and to enter the 

 living organs, or to act again upon the inert silicates and in- 

 soluble vegetable matter,and render portions of them active. 

 It is in this way, that a small quantity of salt introduced into 

 the soil, will continue to reproduce itself, and hence the sur- 

 prising effects which are often witnessed, when salts in small 

 quantities are added to the soil. 



1. The general theory then, of the action of salts, may be 

 thus stated : The bases of salts, whether alkali, alkaline 

 earth, or metallic oxide, act exactly alike '^ that is, (1) They 

 act continually upon the organic matter of the soil, render- 

 ing it soluble and capable of entering the organs of plants. 

 (2) They are taken into the plant, either in combination 

 with their mineral acids, and decomposed by the organic 

 acids, or eliminated directly by the vital force and assimilated. 

 In the latter case, the acid of the salt acts upon silicates as 

 above, and reproduces the same salt. 



2. It will be seen, that if the salt is a carbonate, the car- 

 bonic acid will act with great power upon the silicates. If it 

 is a phosphate or nitrate, both the acid and the alkali are 

 nourishers, and the effect will be much increased. But if the 

 salt is a sulphate, or a hydrochlorate, then the acid will not 

 produce so good effects, and may be poisonous and highly in- 

 jurious, hence the character of the acid determines the char- 

 acter of the effect, or, as it has been expressed, peculiarity of 

 action depends upon the acid and not upon the base of the 

 salt. This is substantially the theory of Dr. Dana. It throws 

 more light on the action of salts, than any which we have 

 seen. It will be further illustrated on the subject of manures. 



