“You haven’t mentioned the apparatus (carburetters) for increasing the richness of the gas, which can be applied by the consumer upon his own premises,” said the old gentleman.

“There is little need.  The burners should be adjusted to the quality of gas furnished.  If there were any real gain in this method of enrichment, the gas companies are the parties who could make the most of it:  indeed, many of them do to such an extent as can be made profitable.  But whenever the temperature of the atmosphere falls, the matter added to the gas is deposited in the pipes, sometimes choking them entirely at the angles.  No:  arrange your burners and regulators to suit the gas that is furnished, demand of the company that it fulfil the law and the contract in regard to the quality of the gas, and give all gas-improving machines the go-by.[3]

“Light having, perhaps, been sufficiently considered for the present needs, we have now to note the effects of the combustion of gas upon the atmosphere, and through this upon the furnishing of rooms and the health of the persons living therein,” said the chemist, again taking up his manuscript.  “The usual products from the combustion of common illuminating gas are carbonic acid, sulphuric acid, ammonia and water-vapor.  Every burner consuming five cubic feet of gas per hour spoils as much air as two full-grown men:  it is therefore evident that the air of a room thus lighted would soon become vitiated if an ample supply of fresh air were not frequently admitted.

“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