The general properties of war,' charcoal are that it is black and brittle and r. ains the form of the wood front which it veil- derived; it is insoluble in water, infusible and on-vola tile in the most intense heat; has of con densing gas as from its power destroy ing bad regarcbd possess ing cottr props-rib It is frequently stated that charcoal is a poor con ductor of heat, but a good conductor of elec tricity; these properties depend on the nature of the charcoal, the lighter wood, such as wil low, yielding a porous charcoal, with little power of conducting heat or electricity; while boxwood yields a very compact charcoal which is a good conductor of heat and electricity. Charcoal never consists entirely of pure carbon, the degree of purity varying directly with the temperature: thus, charcoal charred at 480° contains 65 per cent carbon, while that charred at 750' contains 80, and that charred at 2730' contains 96; but the loss of charcoal occasioned by these high temperatures is very great, the three percentages of charcoal corresponding to these temperatures being 50, 20 and 15.
The uses of wood-charcoal are numerous and extensive. It is very largely used as a fuel, taking in many countries the place of coal. From its being proof against all ordinary chem ical agencies, a superficial charring is frequently resorted to for protecting wood from decay, as in the case of piles driven into mud or into the beds of rivers to serve as foundations. For the same purpose, it is a common practice to char the interior of tubs and casks destined to hold liquids. In a finely-divided state it is commonly regarded as an antiseptic; and there is no doubt that the offensive effluvia from animal matter in an advanced stage of putrefaction disappear when the putrefying substance is covered with a layer of charcoal; but in reality the decay goes on without emission of any odor until at length the whole of the carbon is dissipated as carbonic acid gas, and the hydrogen as water, while the nitrogen remains as nitric acid. It
has been shown that the action consists in a rapid process of oxidation, dependent on the power which finely divided charcoal possesses of condensing oxygen. In a finely divided state, charcoal not only condenses gases to a marvel ous extent, but has the power of absorbing col oring matters, bitter principles, etc.; hence it is of extensive use in the laboratory. From the rapidity of its absorbing action, Stenhouse has proposed to use a respirator filled with charcoal to protect the mouth and nostrils in an infected atmosphere; and the employment of trays of powdered wood-charcoal in 6aq-rooms. in the wards of hospitals and in situations where putrescent animal matter is present. is found to exert a most beneficial influence in sweetening the atmosphere by absorbing and decomposing the offensive gases. These properties render charcoal a valuable material in the construction of filters, not only for decolorizing, but like wise for purifying water for domestic use. It is employed successfully to prevent the escape of noxious vapors at the ventilating openings of sewers, as it allows free passage of air, but condenses the offensive effluvia in its pores where they are destroyed by a process of oxi dation. Besides its use in the manufacture of it has many applications in the arts. edicine it is at present used chiefly to de ctroy fetor, for which purpose it is applied in the form of powder or poultice to gangrenous phagedcnic ulcers. etc.; it is also largely employed in tooth-powders. as by its mechan ical action it removes incrustations. while by its chemical action it destroys fetor of the breath. In indigestion, accompanied by much flatulence, it may be given in of two or three tea spoonfuls suspended in water, or may be ministered in the form of charcoal-biscuits. Very finely divided poplar charcoal is regarded as the best for medicinal uses.