36 



AGRICULTURAL CHEMISTRY, 



We find this nitrogen in the atmosphere, 

 in rain water, and in all kinds of soils, in 

 the form of ammonia, as a product of the 

 decay and putrefaction of preceding genera- 

 tions of animals and vegetables. We find 

 likewise that the proportion of azotised mat- 

 ters in plants is augmented by giving them a 

 larger supply of ammonia conveyed in the 

 form of animal manure. 



No conclusion can then have a better 

 foundation than this, that it is the ammonia 

 of the atmosphere which furnishes nitrogen 

 to plants. 



Carbonic acid, water and ammonia, con- 

 tain the elements necessary for the support 

 of animals and vegetables. The same sub- 

 stances are the ultimate products of the 

 chemical processes of decay and putrefac- 

 tion. All the innumerable products of vi- 

 tality resume, after death, the original form 

 from which they sprung. And thus death 

 the complete dissolution of an existing 

 generation becomes the source of life for a 

 new one. 



CHAPTER VI. 



p 



OF THE INORGANIC CONSTITUENTS OF 

 PLANTS. 



CARBONIC acid, water and ammonia, are 

 necessary for the existence of plants, be- 

 cause they contain the elements from which 

 their organs are formed ; but other sub- 

 stances are likewise requisite for the forma- 

 tion of certain organs destined for special 

 functions peculiar to each family of plants. 

 Plants obtain these subtances from inorganic 

 nature. In the ashes left after the incinera- 

 tion of plants, the same substances are 

 found, although in a changed condition. 



Although the vital principle exercises a 

 great power over chemical forces, yet it 

 does so only by directing the way in which 

 they are to act, and not by changing the 

 laws to which they are subject. Hence 

 when the chemical forces are employed in 

 the processes of vegetable nutrition, they 

 must produce the same results which are 

 observed in ordinary chemical phenomena. 

 The inorganic matter contained in plants 

 must, therefore, be subordinate to the laws 

 which regulate its combinations in common 

 chemical processes. 



The most important division of inorganic 

 substances is that of acids and alkalies. Both 

 of these have a tendency to unite together, 

 and form, neutral compounds, which are 

 termed salts. According to the doctrine of 

 equivalents, these combinations are always 

 effected in definite proportions, that is to 

 eay, one equivalent of an acid always unites 

 with one or two equivalents of a base, v/hat- 

 ever that base may be. Thus 501 -I/ parts 

 by weight of sulphuric acid unite with 1 eq. 

 of potash, and form one eq. of sulphate of 

 pc lash; 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 

 conception 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 con- 

 tains, 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 unites with it. By 

 this is meant, that the quantities in both cases 

 must either be equal or multiples of each 

 other; for the doctrine of equivalents denies 

 the possibility of their uniting in fractional 

 parts. This will be rendered obvious by a 

 consideration of the two following exam- 

 ples: 



100 parts of Cyanic Acid contain 23'26 oxy- 

 gen = 1. 



100 parts of Cyanic Acid saturate 137'21 parts of 

 potash, which contain 23*26 oxygen =1. 



100 parts of Nitric Acid contain 73*85 oxygen =5. 



100 parts of Nitric Acid saturate 214*40 parts of 

 oxide of silver, which contain 14'77 oxygen = 1. 



In the first of these cases, the relation of 

 the oxygen of the base to that of the acid is 

 as 1:1 ; in the second, as 1:5. The capacity 

 for saturation of each acid, is, therefore, the 

 constant quantity of oxygen necessary to 

 neutralize 190 parts of it. 



Many of the inorganic constituents vary 

 according to the soil in which the plants 

 grow, but a certain number of them are in- 

 dispensable to their developement. All sub- 

 stances in solution in a soil are absarbed by 

 the roots of plants, exactly as a sponge im- 

 bibes a liquid, and all that it contains, with- 

 out selection. The substances thus con- 

 veyed to plants are retained in greater or 

 less quantity, or are entirely separated when 

 not suited for assimilation. 



Phosphace of magnesia in combination 

 with ammonia is an invariable constituent 

 of the seeds of all kinds of grasses. It "> 

 contained in the outer horny husk, and is 

 introduced into bread along with the flour, 



