"Remember," said he, looking up from the paper, "that nearly the same effects proceed from the combustion of candles and lamps of every kind when a sufficient number of these are burned to give an equal amount of light. Carbonic acid is easily got rid of, for the rooms where gas is burned usually have sufficient ventilation near the floor by means of a register, or even the slight apertures under the doors--together with their frequent opening--to carry off the small quantity emitted by one or two burners. But there are other gases which must have vent at the upper part of the room, while fresh air should be admitted to supply the place of that which is chemically changed." Returning to his manuscript, he continued: "The burners which give the least light, burning instead with a low, blue flame, form the most carbonic acid and free the most nitrogen. Such are all the burners for heat rather than light. But the formation of sulphuric acid gas may be the same in each. In the yellow flame the carbon particles escape to darken the light colors of the room, not being heated sufficiently to combine with the oxygen. This product of the combustion of gas (free carbon) might be regarded as rather wholesome than otherwise (as its nature is that of an absorbent) were it not the worst kind of dust to breathe--in fact, clogging the lungs to suffocation. In vapor gas--made at low heat--the carbon is in a large degree only mechanically mixed with the hydrogen, and is liable, especially in cold weather, to be deposited in the pipes. This leaves only a very poor, thin gas, mainly hydrogen, which burns with a pale blue flame, as seen in cold spells in winter. High heats and short charges in the retorts of the manufactory give a purer gas and a larger production. Gas made at high heat will reach the consumer in any weather very nearly as rich as when it leaves the gas-holder; for, thus made, the hydrogen and carbon are chemically combined, instead of the hydrogen merely bearing a quantity of carbon-vapor mechanically mixed and liable to deposit with every reduction of temperature. To relieve the atmosphere of the gases and vapors proceeding from combustion is, of course, the purpose of ventilation. The sulphuric acid gas and ammonia will be largely in combination with the water-vapor, which also proceeds from combustion, so that all will be got rid of together. The vaporization of libraries to counteract the excessive dryness (or drying, rather) which causes leather bindings to shrink and to break at the joints, would be of doubtful utility, since it might only serve to carry into the porous leather still more of the gases just mentioned. The action of both sulphuric acid and ammonia is, undoubtedly, to destroy the fibre of leather, so that it crumbles to meal or falls apart in flakes.