THE CULTURE OF FARM CROPS. 



CHAPTEK X. 



CARBONIC ACID. ITS PROPERTIES AND FUNCTIONS 

 IN PLANT GROWTH. 



Carbonic acid is one of the three materials which together 

 form the starting point of vegetable growth ; the others be- 

 ing water and nitric acid. This acid is formed of carbon 

 and oxygen in the proportion of one part of the former to 

 two of the latter chemically combined. It is a colorless gas, 

 having an acid taste and smell; is soluble in water; weighs 

 one-half more than air and can be poured from one vessel 

 to another, as a liquid may be; 100 parts of water dissolve 

 106 parts of this gas, and it is from this source that the roots 

 of plants derive the needed supplies of it. 



It is produced by the combustion of carbon in the atmos- 

 phere; when it unites with oxygen in the proportions men- 

 tioned. An easy way to produce it is to burn charcoal on 

 an open hearth. In a close room this combustion takes the 

 oxygen from the atmosphere and fills the whole space with 

 carbonic acid. This necessarily is a dangerous proceeding 

 and at times causes fatal results, by the keeping of char- 

 coal fires, or even coal fires, in poorly ventilated apart- 

 ments. 



This gas is wholly unable to support life and when exist- 

 ing in an excessive proportion in the air not only destroys 

 animal life, but is also fatal to vegetable existence. Neither 

 will it support combustion. Fire is extinguished by it; but 

 when mixed with certain proportions of hydrogen it be- 

 comes inflammable, and even explosive when mixed with 

 air. It forms a large proportion of the rocks in combina- 

 tion with various mineral elements. One of the most com- 

 mon of the rocks, limestone, and of which marble is one 

 form, contains 44 per cent, of it and can be separated from 

 it by the action of an acid or by burning. If a small quan- 



