66 HOW CROPS FEED. 
Alotropism.—This occurrence of an element in two or even 
more forms is not without other illustrations, and is termed Allotropism, 
Phosphorus occurs in two conditions, viz., red phosphorus, which crys- 
tallizes in rhombohedrons, and like ordinary oxygen is comparatively 
inactive in its affinities ; and colorless phosphorus, which crystallizes in 
octahedrons, and, like ozone, has vigorous tendencies to unite with other 
bodies. Carbon is also found in three allotropic forms, viz., diamond, 
plumbago, and charcoal, which differ exccedingly in their chemical and 
physical characters. 
Ozone Formed by Chemical Action.—Not only is ozone 
produced by electrical disturbance, but it has likewise 
heen shown to originate from chemical action; and, in 
fact, from the very kind of action which it itself so vig- 
orously manifests, viz., oxidation. 
When a clean stick of colorless phosphorus is placed at 
the bottom of a large glass vessel, and is half covered 
with tepid water, there immediately appear white vapors, 
which shortly fill the apparatus. Ina little time the pe- 
culiar odor of ozone is evident, and the air of the vessel 
gives, with iodide-of-potassium-starch-paper, the blue color 
which indicates ozone. In this experiment ordinary oxy- 
gen, in the act of uniting with phosphorus, is partially 
converted into its active modification; and although the 
larger share of the ozone formed is probably destroyed by 
uniting with phosphorus, a portion escapes combination 
and is recognizable in the surrounding air. 
The ozone thus developed is mingled with other bodies, 
(phesphorous acid, etc.,) which cause the white cloud. 
The quantity of ozone that appears in this experiment, 
though very small,—under the most favorable circum- 
stances but '|,,,, of the weight of the air,—is still sufficient 
to exhibit all the reactions that have been described. 
Schénbein has shown that various organic bodies which 
are susceptible of oxidation, viz., citric and tartaric acids, 
when dissolved in water and agitated with air in the sun- 
light for half an hour, acquire the reactions of ozone. 
Ether and alcohol, kept in partially filled bottles, also be- 
come capable of producing oxidizing effects. Many of the 
