Stenhouse has investigated the differences in the absorbent power of different kinds of charcoal; the following are his most important results: 0.5 of a gramme of each kind of charcoal being employed, and the numbers in the table indicating in cubic cen timeters the quantity of absorbed gas.
So rapid is this action of charcoal, that Stenhouse has proposed to use a respirator filled with it to protect the mouth aid nostrils in an infected atmosphere; And the employment of trays of powdered wood•charcoal in dissecting-rooms, in the wards of hospitals, and in situations where putrescent animal matter is present, is found to act very beneficially in purifying the air by absorbing the offensive gases. Its use in refer ence to the filtration of water has been already alluded to.
The determination of the exact specific gravity of the different leases is of great importance in calculating the proportions of the different ingredients of compounds into which they enter; and the whole series of numbers expressing the chemical equiva lents or atomic weights of bodies depend upon the accuracy of the determination of the specific gravity of hydrogen and oxygen.
The following table gives the specific gravity and the weight of 100 cubic in. of some of the most important gases at a barometric pressure of 30 in., and at a temper
ature of 60°, together with the name of the observer! .
The methods employed for determining the specific gravity of a gas, both by direct observation and by calculation, will be noticed in the article SPECIFIC GRAVITY.
As to the chemical properties of gases, most of the different gases, when pure, can be readily distirtguished by some well-marked physical or chemical property. Sonic, are distinguished by their color, others by their peculiar odor; but several of the most important ones—viz., oxygen, nitrogen, hydrogen, carbonic acid, carbonic oxide, light carbureted hydrogen, oletiant gas, and protoxide of nitrogen—require other means for their discrimination. The distinctive characters of the most important gases are noticed in the articles OXYGEN, IIviottoorEN, CHLORINE, etc., and the outlines of the general method of analyzing a gaseous mixture are given in a separate article. For further details on the physical and chemical characters of the gases, we must refer to Miller's Elements of Chemistry, and especially to the volume on Chemical Physics, from which we have borrowed freely; to Kekule's Lehrbuch der Organischen Mende, 1859; and to Ros-' coe's translation of Bunsen's Gasometry.