The expansion of phosphuretted hydrogen by electricity is a subject on which there has been as much diversity as on its absorption. In 1797, Dr. Henry found that it expanded “equally with carbonated hydrogen.” (Philos. Trans.). In 1800, Davy states that phosphuretted hydrogen was not altered in volume by electricity. (Researches, page 303.) In 1810, my experiments led me to adopt the same conclusion. In 1811, Gay Lussac found (Recherches, page 214), that potassium heated in phosphuretted hydrogen gas, expanded 100 volumes to 146; he infers that the true expansion ought to have been to 150. In 1812, Davy observes, that when electric sparks are passed through gases of this kind, “usually there is no change of volume.” (Elements of Chem. Philos. p. 294.) But he adds that when a gas (sp. gr. 6, hyd. being 1) was heated with zinc filings over mercury, there was an expansion of volume of more than ⅓. Also potassium heated in it, made 2 parts become 3 or 3, parts rather more than 4, (1810); the residual gas in these cases was pure hydrogen. Hydrophosphoric gas (sp. gr. 12) yielded 2 volumes of hydrogen, by heating potassium in it. In 1816, Dr. Thomson found that by electric sparks phosphorus was deposited, and hydrogen remained “exactly equal to the original bulk of the phosphuretted hydrogen.” Lastly, in 1817, I found by two experiments, that by electrifying 30 grain measures of phosphuretted hydrogen in a tube over water, uninterruptedly for nearly 2 hours, I produced an expansion of ⅕, or the gas became 36 measures; originally the gas contained 2½ common air, and the rest was combustible so that 100 measures took 190 oxygen. By exploding the residue with oxygen, I found that ¹/₁₅ or ¹/₂₀ of the phosphuretted hydrogen still remained undecomposed. Taking these observations into consideration along with the fact, that 1 volume of the purest gas requires 2 of oxygen for its combustion, I conclude that the true expansion should be ⅓, or 3 volumes of gas should become 4, and then it will be found that ⅓ of the oxygen is joined to the hydrogen and ⅔ to the phosphorus, which accords with what appears to me the only correct view of the constitution of phosphoric acid, namely, 2 atoms of oxygen to 1 of phosphorus. The action of oxymuriatic acid, whether free or combined, on phosphuretted hydrogen, is curious and interesting; in both cases it effects a complete and instantaneous combustion of both phosphorus and hydrogen; when the acid is put to in the state of gas, it not only burns the phosphuretted hydrogen, but any free hydrogen that may be present; but this has a limit: if the phosphuretted hydrogen be largely diluted (90 per cent.) with hydrogen, this last is wholly left; the reason seems to be, the phosphuretted hydrogen burns at a lower temperature; and hence probably it is, that liquid oxymuriate of lime burns the phosphuretted hydrogen, but not the hydrogen gas.