483 



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 |, 1, 

 2, or l 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. 



Some Experiments and Observations on a new Substance which becomes 

 a violet-coloured Gas by Heat. By Sir Humphry Davy, Knt. LL.D. 

 F.R.S. Read January 20, 1814. [Phil Trans. 1814,^. 74.] 



The discovery now announced to the Society was made about two 

 years since by M. Courtois, a manufacturer 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 tw2?/s, violaceous. 



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, 

 metallic 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 pecu- 

 liar 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 fvsed 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 to be red and fusible as in the former experiment. 



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

 2 i 2 



