Page:Proceedings of the Royal Society of London Vol 1.djvu/503

Rh laws of multiple proportions, Sir Humphry Davy observes, that the fact is, that the oxygen which Professor Berzelius supposes to be in the chlorine is combined with the metals; and that with respect to any regularities among multiple proportions, there is no general law observable. Azote, for instance, combines with three volumes of hydrogen. When combined with oxygen it may be united to 4%, 1, 2, or 1% of the same body, and in combination with chlorine it unites with four volumes.

The author combats the notion of oxygen being considered as the principle of acidity, and contends that hydrogen enters into the com- position of nearly as many acids as oxygen; that chlorine and ﬂuorine are merely bodies of the same class, which like oxygen combine with great energy, but do not owe these properties to the presence of any oxygen contained in them.

The discovery now announced to the Society was made about two years since by hi. Courtcis, a manufairturer of saltpetre at Paris. It is procured from the ashes of sea-weeds: after the extraction of the carbonate of soda, the addition of strong sulphuric acid extricates this substance in the form of a violet vapour, which condenses in crystals, that have the colour and lustre of plumbago. The colour of its vapour has occasioned the French chemists to give it the name of iode. from 2.35115, violaceaus.

Specimens of this substance were given to MM. Desormes and Clement, who have given a memoir upon it to the Imperial Institute, describing its principal properties. Its speciﬁc gravity is said to be about 4. It volatilizes at a temperature rather below that of boiling water. It combines with phosphorus, with sulphur, with metals, metach oxides, and with alkalies, forming with ammonia a detonating compound. It dissolves in alcohol, or ether; and with hydrogen it forms a compound very similar to muriatic acid gas, but which M. Gay-Lussac, in a memoir read to the Institute, shows to be a peculiar acid, distinct from the muriatic: and he compares the body itself to oxymuriatic acid or chlorine; for, like that body, it may either be supposed simple, or thought to contain oxygen.

Sir Humphry Davy’s ﬁrst trial was, whether muriate of silver could be formed from it; and he found that the precipitate occasioned by it from nitrate of silver differed from the muriate in being yellow when ﬁrst formed, and red when fused by a moderate heat. This compound was decomposed by Essed hydrate of potash, or solution of potash, and gave an oxide of silver, the oxygen of which is ascribed by the author to the presence of water. This compound of iode and silver was also formed by direct action of the purple vapour on silver leaf, and was found tobe red and fusible as in the former experiment.

Potassium heated in the vapour, burns slowly with a pale blue