166 On Ozone and its Relations to 
our wants? But in it we also possess a tender guardian, 
gently abstracting from its bosom the very essence of life ; ” 
and still more gently, day by day, feeding the tender plant, 
and satisfying the thirsty forest with their daily wants— 
breathing to us the very spirit of life—and even then its ~ 
mission is not expended ; it is finally ordained to enshrine, 
as in a pall, the deadly putrefaction, fatal and yet co- 
existent with such grandeur. 
The active energy of ozone in the atmosphere may be 
directly observed in many ways in its prejudicial behaviour 
to artificial and manufactured products. Metallic sub- 
stances, iron more especially, quickly becomes oxidized if 
alternately exposed to water and the atmosphere, owing to 
the generation of ozone. Water boiled in iron vessels is 
known speedily to destroy such by continued rusting; the 
decay of stonework and timber may be equally attributable 
to the same cause. In the natural purification of water, 
evaporation and the generation of ozone thereby is promi- 
nently manifest ; the soil through which the water perco- 
lates consisting of an absorbent material and possessing no 
actual ozonizing properties, simply brings the liquid into 
more intimate contact with the air and promotes evapora- 
tion. On this principle the old systems of artificial filtra- 
tion through gravel and sand, and other finely divided 
substances owe their virtue. From the foregoing remarks 
it is evident, also, that by boiling water containing organic 
impurity much becomes oxidized by ozone; but neither 
instance will bear comparison with the effects produced by 
animal charcoal. 
Animal charcoal, or bone black, consists of carbon and 
phosphate of lime principally, but also in conjunction with 
many minor substances, of which carbonate of lime is the 
most prominent. To be of good quality it should present 
a dullish cast, and not suffer any loss from organic matter by 
exposure to a dull red heat in a closed retort. On ignitiona 
purely white residue should remain; if clayey matter or 
metallic oxides be present they will be conspicuous on the 
surface after ignition, and the charcoal has, in all proba- 
bility, been previously employed for filtering purposes. 
The proportion of actual carbon present in the average 
quality of animal charcoal is about 20 per cent. (Sten- 
house), the remaining per centage consisting chiefly of 
phosphates of lime and magnesia. Newly burned charcoal 
is remarkable for its great absorbent power, both for gases 
and liquids. Ifatest glass be filled with water, a large 
