Animal Charcoal. 159 
and give the characteristic purple tint. It is, however, 
destroyed in the presence of a free acid. Owing to its 
affinity for oxygen, the pulverized gum, as just mentioned, 
becomes green in contact with the air by combining with 
the oxygen therein. If the clear solution of the gum ex- 
posed to the air be observed horizontally under the surface, 
with the light coming ina perpendicular direction from above, 
a purple halo appears for a depth of about one-sixteenth 
of an inch, it cannot be detected when looked at from 
above. Freshly precipitated gum, from its solution by 
means of water or otherwise, if free from oxyyen when pre- 
cipitated, soon absorbs sufficient from the atmosphere to 
turn it green: the effects described hereafter should, 
for this reason, be observed shortly after the experi- 
ment. 
Dr. Stenhouse and others have shown that animal, in 
common with other charcoal, possesses a peculiar property 
of condensing on its surface gaseous oxygen and convert- 
ing itinto ozone, and yet the ozone, which is known asa 
transmissable substance, is difficult and if not impossible to 
separate in its normal state from the locality of its genera- 
tion. The presence and actual contact of charcoal as a 
disinfectant is well known, and an instance scarcely exists 
in which the virtue of its properties has been known to 
affect their influence beyond the immediate proximity of 
the substance. The following experimental illustration 
may, however, show the fact more forcibly :—A long tube 
is filled with fine grained dry charcoal, anda current of 
atmospheric air passed slowly through it, on leaving the 
tube the air will be found to contain no greater quantity of 
ozone than previous to its entrance. If the charcoal be 
then moistened with spirit or water, still no additional trace 
of ozone will be found. The air, however, is neither 
deprived of any sensible amount of ozone, and yet the 
charcoal, during the process, possessed the full virtue of 
the ozoning properties. Under varying temperatures also 
no important alteration of weight is perceptible, for the 
substances are but mechanically mixed, and a slight dis- 
turbance would be sufficient to alter their composition on 
this assumption, and vary the proportion of gaseous ozone 
and charcoal. Independently of these instances it is im- 
possible for a substance to exist in the pores or surface of 
the charcoal when employed asa filtering material and 
saturated with the liquid under operation, or if possible to 
exist, it could hardly be replenished when exhausted by 
P 2 
