BICHLORIDE OR METHYLENE AS A GENERAL ANESTHETIC. 235 
position indicated. A considerable number of methyl compounds have been 
successively the subject of experiment in Dr. Richardson’s hands, but it is 
the substance indicated above, the bichloride of methylene, which recom¬ 
mends itself most strongly. 
Bichloride of methylene is represented as a fluid possessing a sweet ethe¬ 
real odour, resembling that of chloroform, and boiling at 88° Fahr.; it has a 
specific gravity F34. Chloroform and tetrachloride of carbon have both, as 
might be anticipated, higher densities and boiling-points. Chloroform boils 
at 142°, its specific gravity is 1'49; whilst tetrachloride of carbon has a den¬ 
sity of 159, and boils at 172°. 
Dr. Richardson, in his lecture, pointed out the relations which, it is well 
known, exist between these substances. The series of compounds of which 
chloroform, tetrachloride of carbon, and bichloride of methylene are mem¬ 
bers, takes as its starting point marsh-gas, or, as it is frequently termed, the 
hydride of methyl. This is generally represented as containing a radicle, 
called methyl, C H 3 , in combination with hydrogen; and, consequently, its 
formula is usually written C H 3 H ( = CH 4 ). 
In accordance with the remarkable law of substitution, we may produce 
from this compound a complete series of derivatives which are all formed 
upon the same type, all possessing, so to speak, the same molecular figure, 
and their formulae exhibit a corresponding symmetry. By the action of 
chlorine, duly controlled and modified, it is possible to remove all the four 
atoms of hydrogen by successive steps, and simultaneously to introduce 
chlorine, atom for atom, into their place, in such a manner that it becomes 
substituted for them. 
By extracting in this fashion one atom of hydrogen, replacing it by one 
atom of chlorine, we obtain a body which is gaseous at all ordinary tem¬ 
peratures, and is known as chloride of methyl, CH 3 C1. Two atoms of hy¬ 
drogen may be similarly substituted by two atoms of chlorine, producing the 
newly proposed anaesthetic, bichloride of methylene or chloride of monoehlor- 
inethyl, CH 2 C1 2 . By a third step, three atoms of hydrogen may be taken 
out and their position filled by the corresponding number of chlorine atoms 
yielding the so-called terchloride of formyle, CHC1 3 , ordinary chloroform. 
And lastly, the whole of the hydrogen may be represented by chlorine, and 
we arrive at the compound CC1 4 , the tetrachloride of carbon. 
These successive steps may be viewed at a glance by placing the five for¬ 
mulae in juxtaposition:— 
CH 3 H = CHHHH. Marsh-gas. 
CH 3 C1 = CHHHC1. Chloride of methyl. 
C Ho Cl Cl = CHHC1C1. Bichloride of methylene. 
CHCLCl = CHC1C1C1. Chloroform. 
CC1 3 C1 = CC1C1C1C1. Tetrachloride of carbon. 
The fourth and fifth of these compounds are already well known anaesthe¬ 
tics ; it is now the third on the list, the bichloride of methylene, which has 
recently been the subject of Dr. Richardson’s most successful experiments. 
The process of direct substitution alluded to above is of course interest¬ 
ing only from the theoretical side of the question. Practically, the prepara¬ 
tion of all the four chlorine derivations described is effected by indirect means. 
The hydride of methyl is a compound occurring in nature, and also found 
among the gases of coal mines, and in that situation constitutes fire-damp. 
It may be made artificially by heating a mixture of an acetate, usually ace¬ 
tate of sodium, with an excess of caustic potash and lime. Dr. Richardson 
has elsewhere described the effects of inhaling this gas. It appears that an 
atmosphere very highly charged with it may be breathed with impunity for 
a short time, and when at last death results from its continuance, it comes on 
