76 HOW CROPS FEED. 
tricity directly, but the ozone developed by it, accom- 
plishes this oxidation. It has long been known that nitric 
peroxide decomposes with water, yitiding nitric and ni- 
trous acids thus: 
2NO, + H,O .=. NOT +23 
It is further known that nitrous acid, both in the free 
state and in combination, is instantly oxidized to nitric 
aci:l by contact with ozone. 
Thus is explained the ancient observation, first made by 
Cavendish in 1734, that when electrical sparks are trans- 
mitted through moist air, confined over solution of potash, 
nitrate of potash is formed. (For information regarding 
this salt, see p. 252.) 
Until recently, it has been supposed that nitric acid is 
present in only those rains which accompany thunder- 
storms. 
It appears, however, from the analyses of both Way and 
Boussingault, that visible or andible electric discharges 
do not perceptibly influence the proportion of nitric acid 
in the air; the rains accompanying thunder-storms not 
being always nor usually richer in this substance than 
others. 
Von Babo and Meissner have demonstrated that sélent 
electrical discharges develop more ozone than flashes of 
lightning. Meissner has shown that the electric spark 
causes the copious formation of nitric peroxide in its im- 
mediate path by virtue of the heat it excites, which in- 
creases the energy of the ozone simultaneously produced, 
and causes it to expend itself at once in the oxidation of 
nitrogen. Boussingault informs us that in some of the 
tropical regions of South America audible electrical dis- 
charges are continually taking place throughout the whole 
year. In our latitudes electrical disturbance is perpetu- 
ally occurring, but equalizes itself mostly by silent dis- 
charge. The ozone thus noiselessly developed, though 
operating at a lower temperature, and therefore more 
