52. Charcoal. One of the most valuable forms of carbon is charcoal;
valuable not in the sense that it costs hundreds of dollars, but in
the more vital sense, that its use adds to the cleanliness, comfort,
and health of man.

The foul, bad-smelling gases which arise from sewers can be prevented
from escaping and passing to streets and buildings by placing charcoal
filters at the sewer exits. Charcoal is porous and absorbs foul gases,
and thus keeps the region surrounding sewers sweet and clean and free
of odor. Good housekeepers drop small bits of charcoal into vases of
flowers to prevent discoloration of the water and the odor of decaying
stems.

If impure water filters through charcoal, it emerges pure, having left
its impurities in the pores of the charcoal. Practically all household
filters of drinking water are made of charcoal. But such a device may
be a source of disease instead of a prevention of disease, unless the
filter is regularly cleaned or renewed. This is because the pores soon
become clogged with the impurities, and unless they are cleaned, the
water which flows through the filter passes through a bed of
impurities and becomes contaminated rather than purified. Frequent
cleansing or renewal of the filter removes this difficulty.

Commercially, charcoal is used on a large scale in the refining of
sugars, sirups, and oils. Sugar, whether it comes from the maple tree,
or the sugar cane, or the beet, is dark colored. It is whitened by
passage through filters of finely pulverized charcoal. Cider and
vinegar are likewise cleared by passage through charcoal.

The value of carbon, in the form of charcoal, as a purifier is very