METH YLENE, BICITLORIDE or (Calla, C12), is an organic compound which has recently attracted much attention from its value as an anxsthetie agent. Dr. Richardson, who has long been studying the physiolorrical properties of the methyl-compounds, with the view of finding amongst them a safer compound than ehloroforrn, believes, from his experiments on animals, that in the subject of this article he has found such a com pound. As the deaths from chloroform may be computed, according to him, at one in. 1500 administrations, it is obvious that there is reason for searching for a still safer anmstlietie agent. Dr. Snow, as is well known, thought that he had discovered an almost positively safe agent in amylene (C, otho); but the value of more than 200 safe adminis trations was at once destroyed by two rapidly succeeding deaths; and hence a large number of successful cases of the new wrent 'must bc reported before it will displace chloroform from its present well-deserve4osition. In the article on methyl (q.v.), we have shown that the composition of hydride of methyl (or marsh gas) is expressed by CalI2,II, which may be written C21111HH. Now, according to the theory of substi tutions, one, two, three, or even all four of the atoms of hydrogen may be replaced by a corresponding number of atoms of chlorine. Thus (a), if one atom of H be replaced by one atom of Cl, we have chloride of methyl, C2113CI; (b) if two atoms of H are replaced by two atoms of Cl, the resulting compound is &Chloride of methylene, C2112012, the C2H, here representing a new radical termed methylene, of which very little is knOwn; (c) if three atoms of 11 Pre replaced by three atoms of Cl, the resulting compound is terchloride of formyle, C2HC13, or common chloroform, another radical, viz., formyle, C211, now appearing; (d) if the whole of the H is replaced by Cl, the resulting com pound is tetrachloride of carbon, CC14. We thus have four new bodies which may be constructed step by step out of hydride of methyl or marsh gas, and similarly, by start ing with tetrachloride of carbon, the chemist may re,trace the individual stages till he gets back to marsh gas. All these derivatives of marsh gas possess the power of pro
ducing antesthesia when they are inhaled as vapor by men and animals. That the latter two—viz., chloroform and tetrachloride of carbon—possess this power, has been long known, Dr. P. Smith having especially directed attention to the properties of the last named compound; but that the first two also exert the sanie influence is a fact new to science, for which we are indebted to Dr. Richardson. " I discovered," he observes, " that chloride of methyl was a certain and gentle amesthetic in July  last, and this led me to hope that something more stable and manageable could be obtained—some thing that should stand between the chloride of methyl and chloroform. That substance is now found in the bichloride of methylene. That till:, compound would produce rapid, safe, and easy general anmsthesia, I discovered by experiment ou Aug. 30 of the present year."—Ifed. Times, Oct. 19, 1867.
It is a colorless fluid, having an odor like that of chloroform; and is pleasant to inhale, as it causes little irritation 1.6 the mucoug membrane, It boils at 88°, and has a. spec. gr. of 1.344, while that of its vaPor is 2:937 (or nea.rly three times that of air)z Hence, it boils at a lower temperature than other anwsthetics; while its specific gravity, both as a liquid and a vapor, is lower than that of chloroform, but much higher than that of ether; hence, from its easier evaporation, it requires more free administration than chloroform, and, from its greater vapor-density, it should be given less freely than ether. It mixes readily with absolute ether, and this combination yields a vapor con taining corresponding proportions of each, their boiling-points only differing at most by 4°. It also combines with chloroform in all proportions. It should have a neutral reac tion to test-paper. If a trace of acid be present--which is possible, but not probable— its inhalation might prove dangerous. To prevent decomposition, it should, like chloro form, be well guarded from the action of light.