G2 DEODORIZERS AND DISINFECTANTS. 
It is not our intention now to speak of food and its 
changes as productive of diseases, but of the action of those 
agents which correct a vitiated state of the atmosphere 
arising from the presence of adventitious matters in it, under 
the head of deodorizers and disinfectants. 
These terms must not be accepted as interchangeable ones, 
since some bodies merely absorb poisonous or fetid effluvia, 
and may be said to act mechanically ; while others both 
absorb and decompose the pernicious gases, and such ope- 
rate chemically . Those that simply imbibe and retain these 
compounds can be made to give them up again, and that 
sometimes altogether unchanged ; hence they become only 
deodorizers ; while those which decompose them, thus ren- 
dering them inert, are true disinfectants. Even sawdust is 
known to abstract fetor from the air, and likewise plaster of 
Paris, but each only to a small extent. Sulphate of iron has 
also been used for the same purpose; but there are some 
objections to the employment of it. Gravel and sand are 
admirable deodorizers. This is seen in the making of filter- 
ing beds for water. Doubtless nature carries on a similar 
process on a larger scale ; hence water that has passed 
through siliceous strata is generally pure. The manner in 
which this purification is brought about appears not to be 
clearly understood ; for although some persons have sup- 
posed the action to be merely mechanical, this can hardly be 
the case, since the water holds in solution most of the 
different substances by which it is contaminated. Those 
that are only suspended in it are, of course, by this means 
readily separated. Others have referred it to what is called 
surface action ; such as obtains in the condensation of gases 
by charcoal, hence its value as a deodorizer; or that which 
takes place when oxygen and hydrogen are induced to unite 
by means of platinum, their atoms being by this means 
* brought within the sphere of each other's attractive force. 
And again others to the influence of oxygen as it exists in 
the air, which gradually effects the destruction of the sub- 
stances, or slowly burns them up. Markedly is this seen in 
that form of oxygen called ozone, which by its oxidating 
properties forms with the elements of the organic molecules, 
water and carbonic acid ; while at the same time ammonia 
results from the union of the nitrogen with hydrogen. In 
like manner proto-salts are quickly changed by it into per- 
salts, sulphurets into sulphates, nitrous acid into nitric acid, 
and so on. The use of ozone in the air is for the purpose 
of correcting miasm. If, however, it be in excess or in 
diminished quantities, then diseases result, but of precisely 
