forms an explosive mixture, as it does also when mixed in certain proportions with air; but when burned through a very small tip and under slight pressure, or when mixed with coal gas or air in proper proportions, an exceedingly brilliant and highly luminous flame is produced. Acetylene is poisonous, combining with the hæmoglobin of the blood, to the exclusion of oxygen, to form a compound similar to that yielded by carbon monoxide. Moissan, however, reports that when prepared from pure calcium carbide, and after being purified by liquefaction, it has an ethereal odor, and can be breathed in small quantities without evil effects. Regarding its explosiveness Mr. J. M. Crafts says: "Experiments, using a two-inch gas pipe as a cannon, show that from five to six per cent of acetylene mixed with air forms an explosive mixture. . . . About ten per cent of water gas is necessary before an explosive mixture with air is formed." Explosive mixtures in the air of a room would be produced by much smaller percentages than these. Lechattelier gives 2·8 per cent acetylene mixed with air as an explosive compound. So far as its poisonous qualities are concerned, acetylene seems to have a little the advantage of water gas; the poisonous principle of the latter is carbon monoxide, whose combination with the blood is somewhat more energetic than that of acetylene, and which has no odor to serve as a warning in case of a leak, as has acetylene. Acetylene is, however, more prone to form explosive mixtures. This is due to the fact that in the combination of carbon and hydrogen to form acetylene 61·100 units of heat are absorbed. Thus the heating power of a cubic foot of acetylene is sufficient to raise 407 kilogrammes (a kilogramme = 2·2 pounds) of water 1° C. The combustion of the same amounts of uncombined carbon and hydrogen as are present in a cubic foot of acetylene will raise only 336·5 kilogrammes of water to 1° C, leaving a difference in favor of acetylene of 70·5 heat units—the unit being the amount of heat required to raise the temperature of one kilogramme of water 1° C.
Acetylene is one of the important bodies, much used by the chemist in the synthesis of organic compounds. It is also reported to be of value in polariscope work, permitting the reading of solutions so highly colored as to be opaque to the ordinary sources of light. Some interesting experiments with the gas in abnormal physical states were recently performed by J. J. Suckert, during a lecture before the Franklin Institute. A tube of liquefied acetylene was cooled to-28° F., and then the pressure removed. Rapid evaporation took place, and a portion of the liquid gas was solidified into a snowlike mass whose temperature was found to be-118° F. A part of this snow placed on some mercury in a saucer soon froze the latter, and another portion, on being dropped into water, upon which it floated, gave off acetylene