with that relating to the difficulty of combustion of the combined vapors, I have used largely in these researches the mixture of chloroform and carbon bisulphide. The combined vapors produce also a singularly good antiseptic atmosphere.
Coal-Gas.—Common coal-gas is one of the most potent of narcotizing gases. It is a compound of four gases, three of which are excellent narcotics, and one a negative gas—forty-seven per cent of hydrogen, forty-two of marsh-gas, three of heavy hydrocarbons, and eight of carbonic oxide. All these gases are anaesthetic in their action: marsh-gas is one of the best, and carbonic oxide is one of the quickest; but they are all explosive.
For the lethal purpose, nothing could possibly surpass coal-gas. I put it freely to the test, and found it was all that we could desire. In an atmosphere containing twenty-five per cent of this gas, an animal goes to sleep in from two to three minutes, and dies asleep as easily as in any narcotic vapor or gas whatever. The gas is always at hand, and for the present purpose is the cheapest and readiest of all. Under such circumstances, it seems absurd to think of going any further for a narcotic agent. And yet it is necessary, at all events, when a large lethal chamber is wanted, on account of the danger from explosion. All things considered, I was led to conclude that carbonic oxide was the best narcotic agent to employ, combining it with chloroform or carbon bisulphide, if that should prove necessary. Deciding on this point, the next question was how to manufacture the carbonic oxide so as to bring it into practical use on the easiest as well as the largest scale.
After making some unsatisfactory experiments, I luckily recalled Mr. Clark's condensing-stove. This is a most ingenious invention. The fumes proceeding from the combustion in the furnace first ascend and then descend through two lateral columns, to escape by a tube directed over a trough or saucer. A large quantity of water-vapor is in this way condensed, and is collected at the base of the stove, together with substances derived from the combustion, which are soluble in water. Here, with a little modification, was what I wanted. To adapt the stove to my purpose, I got Mr. Clark to make a charcoal furnace over a gas-burner, so that, when the charcoal was laid in the furnace, it could be instantly set alight by merely turning on and lighting the gas, letting the flames of gas play through the charcoal. Next I got him to make a large condensing cistern beneath the stove, with an opening from it to convey the carbonic oxide by a tube into the lethal chamber, and with a tap, by which the condensed fluid could be drawn off. The arrangement answered straight away, if I may so say. The immediate combustion of the charcoal by the gas yielded very nearly the theoretical value of the product, carbonic oxide. The gas was deprived of water by the condensation; it was delivered over to the chamber with a steadiness sufficient for all practical necessities;
