886 M,Bahrdy on a peculiar Substance in Sea Water. [Nov. 



pounds of hydrogen when they are dissolved in watery and hy- 

 drobromic acid is formed at their expense. 



3. Hydrobromic acid may be procured by decomposing the 

 cubic crystals of brome and potash with sulphuric acid, but the 

 gas so obtained is often mixed with a small quantity of sul- 

 phurous and muriatic acid gases, which prevents the employ- 

 ment of this method when the hydrobromic acid is wanted per- 

 fectly pure. 



4. To obtain this acid in a state of purity, I had recourse to 

 a process, borrowed to a certain extent from that which is em- 

 ployed for the preparation of hydriodic acid gas. Brome and 

 phosphorus when put together and moistened with a few drops 

 of water, give out an abundance of hydrobromic acid gas, 

 which may be received over mercury. 



Hydrobromic acid gas is colourless, its taste is quite acid. 

 When exposed to the air it exhales white vapours, which are 

 denser than those produced in the same way from muriatic acid. 

 These vapours have a very penetrating smell, and occasion vio- 

 lent coughing. 



Hydrobromic acid is not decomposed when it is passed 

 through a red hot tube of glass ; nor does it suffer decom- 

 position if previously mixed with oxygen, and then passed 

 through the red hot tube, nor is any effect produced by putting 

 a taper in the mixture. 



On the other hand, brome does not appear to be capable of 

 decomposing water, as chlorine does. I did not find either that 

 oxygen was disengaged, or hydrobromic acid formed, by passing 

 brome and the vapour of water through a red hot glass tube. 



Hydrobromic acid is decomposable by chlorine, which, uniting 

 with its hydrogen, produces immediately abundant orange red 

 vapours, and a deposition of small drops of brome. In ope- 

 rating over mercury these drops are soon absorbed by the 

 metal, and the gaseous matter which remains after the action 

 possesses all the characters of muriatic acid. Certain metals 

 also decompose hydrobromic acid gas. It appeared that when 

 it was pure, mercury did not occasion any alteration ; but tin 

 and potassium decomposed it entirely, the first at a moderately 

 high, and the latter at the usual temperature. A fragment of 

 potassium passed into a graduated tube full of this gas loses its 

 metallic brilliancy in a few seconds, and is converted into a 

 white matter which gives out brome by the action of chlo- 

 rine; the volume of the gas is exactly reduced to one half 

 in this experiment, and the residual gas is hydrogen ; according 

 to this experiment hydrobromic acid gas is similarly constituted 

 to hydriodic and muriatic acid gases ; that is to say, it is formed 

 of equal volumes of hydrogen gas and the vapour of brome, 

 without either increase or diminution of volume. 



