182 



ELEMENTARY SUBSTANCES FORMED IN THE ASH. 



subsidiary questions, which will hereafter present themselves to our 

 notice. 



§ 3. Of the several elementary bodies usually met ivith in the ash of plants 

 What is understood by the term element or elementary body among 

 chemists has already been explained (Lect. I., p. 22), as well as the 

 number and names of those elements with which we are at present ac- 

 quainted. 



Of »hese elementary bodies we have seen that the organic part of plants 

 contains rarely more than four, namely, carbon, hydrogen, oxygen, and 

 nitrogen, in various proportions. In the inorganic part there occur nine 

 or ten others, generally in combination, either with oxygen or with one 

 another. 



The names of these inorganic elements are as follow : 



Other elementary bodies, chiefly metallic, occur in some plants — occa- 

 sionally, and in very small quantity, — but, so far as is yet known, they do 

 not appear to be either necessary to their growth, or to exercise any ma- 

 terial influence on the general vegetation of the globe. 



Of all the above elementary bodies it may be said, generally, 



1°. That with the exception of sulphur,f they are not known to exist 

 or to be evolved, in any (juantity, anywhere on the surface of the globe, 

 in their simple, elementary, or uncombined state; and that, therefore, 

 in this state they in no way affect the progress of vegetable growth, or 

 require to occupy the attention of the practical agriculturist. 



2°. They all, however, exist in nature more or less abundantly in a 

 state of combination with other substances, and chiefly with oxygen, [for 

 an explanation of the meaning and of the laws of chemical combination^ 

 see Lecture II., p. 32] — but in no state of combination are they known 

 to be generally diffused through the atmosphere of the globe, so as to be 



* Called also Hydro-sulphuric Acid. 



» Given off in vapour from active volcanoes, and from rents and fissures m ancient volcanic 

 countries. 



