106 OF THE INORGANIC CONSTITUENTS OF PLANTS. 





must, therefore, be subordinate to the laws which 

 regulate its combinations in common chemical pro- 

 cesses. 



The most importaift division of inorganic substan- 

 ces is that of acids and alkalies. Both of these have 

 a tendency to unite together, and form neutral com- 

 pounds, which are termed salts. According to the 

 doctrine of equivalents, these combinations are al- 

 ways effected in definite proportions, that is to say, 

 one equivalent of an acid always unites with one or 

 two equivalents of a base, whatever that base may 

 be. Thus 501*17 parts by weight of sulphuric acid 

 unite with 1 eq. of potash, and form 1 eq. of sulphate 

 of potash ; the same quantity unites with 1 eq. of 

 soda, and produces sulphate of soda. From this 

 fact follows the rule, — that the quantity, which an 

 acid requires of an alkali for its saturation, may be 

 represented by a very simple number. 



It is perfectly necessary to form a proper concep- 

 tion of what chemists denominate the " capacity 

 for saturation of an acid," before we are able to 

 form a correct idea of the functions performed in 

 plants, by their inorganic constituents. The power 

 of a base to neutralize an acid does not depend 

 upon the quantity of radical which it contains, but 

 altogether upon the quantity of its oxygen. Thus 

 protoxide of iron contains 1 eq. of oxygen, and 

 unites with 1 eq. of sulphuric acid in forming a 

 neutral salt ; but peroxide of iron contains 3 eq. of 

 oxygen, and requires 3 eq. of the same acid for its 

 neutralization. Hence when a given weight of an 

 acid is neutralized by different bases, the quantity 

 of oxygen contained in these bases must be the 

 same as is exhibited by the following scale : — 



501*17 parts of Sulphuric Acid neutralize 258-35 Magnesia Oxygen = 100 

 " " " 647-29 Strontia " =100 



" " " 1451-61 Oxide of Silver " =100 



« '* " 956-8 Barytes " =100 



It follows from the law of equivalents, that the 

 quantity of oxygen in a base must stand in a simple 

 relation to the quantity of oxygen in an acid which 



