Note 1 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

The character of sulphur is very clearly defined in the organo-metallic compounds. Not to dwell on this vast subject, which belongs to the province of organic chemistry, I think it will be sufficient for our purpose to compare the physical properties of the ethyl compounds of mercury, zinc, sulphur and oxygen. The composition of all of them is expressed by the general formula (C2H5)2R, where R = Hg, Zn, S, or O. They are all volatile: mercury ethyl, Hg(C2H5)2, boils at 159°, its sp. gr. is 2·444, molecular volume = 106; zinc ethyl boils at 118°, sp. gr. 1·882, volume 101; ethyl sulphide, S(C2H5)2, boils at 90°, sp. gr. 0·825, volume 107; common ether, or ethyl oxide, O(C2H5)2, boils at 35°, sp. gr. 0·736, volume 101, in addition to which diethyl itself, (C2H5)2 = C4H10, boils about 0°, sp. gr. about 0·62, volume about 94. Thus the substitution of Hg, S, and O scarcely changes the volume, notwithstanding the difference of the weights; the physical influence, if one may so express oneself, of these elements, which are so very different in their atomic weights, is almost alike.