144 LECTURES ON 



vegetation of former times, or, indeed, of pre-Adamite epochs. It 

 it is calculated that the carbonic acid yearly produced by the consump- 

 tion of bituminous and anthracite coals in Great Britain amounts to 

 fifty millions of tons, a quantity capable of supplying carbon to seven- 

 eighths of all the cultivated crops of that country. 



"The deficit of nitrogen-compounds is made up in part by electrical 

 discharges in the atmosphere. Cavendish was the first to notice that 

 the electric spark causes nitrogen and oxygen, in a state of mixture, 

 to combine into nitric acid. In accordance with this observation, it 

 is found that the rain which falls during thunder storms contains more 

 nitric acid than at other times. Although in our latitude the amount 

 of plant food thus formed may be very trifling, it is possibly other- 

 wise in tropical regions, where, according to the testimony of trav- 

 ellers, the rumbling of thunder may be heard at any hour of the day 

 during a considerable portion of the year. 



The conversion of free nitrogen into ammonia is not known to take 

 place in the atmosphere, nor are we certain that it is accomplished in 

 the soil. It has, indeed, been asserted by Hermann and Mulder that, 

 during the decay of wood, hydrogen is evolved, which, at the mo- 

 ment of liberation, unites itself to nitrogen with the production of 

 ammonia, but the experiments on which this assumption was based 

 do not now appear to be worthy of confidence. 



In the soil, however, there does occur a constant formation of nitric 

 acid, especially where lime or other alkaline bodies are present that 

 may combine with it. It appears, indeed, that the greater share of 

 this nitric acid results from the oxydation of the nitrogen of organic 

 debris, but it is probable that the free atmospheric nitrogen is, to 

 some extent, involved. 



"When electrical discharges are made to pass through the air or 

 through pure oxygen gas, the latter shortly acquires entirely new 

 properties. The most remarkable change it undergoes consists in its 

 obtaining a powerful and peculiar odor, the same which is so often 

 perceived near where lightning has struck. The oxygen, thus modi- 

 fied, is found to be capable of much more rapid and intense action 

 upon other bodies than is exerted by ordinary oxygen. It at once 

 oxydizes ammonia to nitric acid and water, and also, in presence of 

 an alkali or lime, unites direct with free nitrogen producing a nitrate. 

 Oxygen thus altered, and intensified in its affinities, is termed ozone 

 or active oxygen, and not only is it produced by electricity, but like- 

 wise by certain processes of oxydation. When phosphorus slowly 

 oxydizes in the air, when the oils of turpentine and bitter almonds 

 are exposed to the atmosphere for a time, the same ozonization oc- 

 curs. Schoenbein, to whose assiduous researches we owe these highly 

 interesting facts, is of the opinion that all instances of nitrification 

 are due to the action of ozone. Although we are not as yet able to 

 make a probable estimate of the amount of free nitrogen that is thus 

 oxydized in any given time, or to form any notion of the quantitative 

 importance of the effects of this agent, we have the satisfaction of 

 standing on a threshold which promises us an entrance into the full 



