DECOMPOSITION OF FLUORIC ACID. $j[ 



tber the fttioric gas holding in solution boraeic acid ; or ra- 

 ther the siliceous fluoric gas, because the foreign matter in 

 this, containing nothing combustible, cannot lead us into 

 errour, and can be of no injury farther than giving an ad- 

 dition of this matter. Accordingly we employed, these 

 gasses, and chiefly the siliceous fluoric gas, in our experi- 

 ments on the decomposition of the fluoric acid, of which we 

 shall now proceed to give an account. 



When the metal of potash is placed, in contact with sil}- Action of p»* 



ceous fluoric £as at the common temperature, it undergoes tass5u ™ ori sii ** 



3 L a ceous Suonc 



no perceptible alteration, except becoming slightly dull on ga*. 



the surface : but if it be melted, it soori thickens, and 

 burns vividly, with the extrication of much heat and light. 

 In this combustion there is a great absorption of fluoric 

 acid, very little hidrogen gas is disengaged, the metal dis- 

 appears, and a solid substance of a reddish brown colour is 

 produced. 



If this substance be treated with cold water, hidrogen The prcduo? 

 gas is evolved, though it appears no longer to contain any treated ^tfc 

 metal. If, after having treated it with cold water, it is 

 treated with hot, more hidrogen gas is evolved, but less 

 than the first time j and on the whole scarcely a third as 

 much as the metal itself would yield with water is obtained. 

 If the waters of elutriation be added together and evapO- 

 rated, we obtain from them nothing but fluate of potash 

 with excess of alkali; and if we examine the residuum, 

 which, when well washed, is still of a reddish brown colour, 

 we fiud it to possess the following properties. When thrown fcpsiduuni 

 into a silver crucible at a cherry red heat, it burns vividly, burned in aif * 

 and disengages a little acid gas ; after which, from being 

 insoluble in water, it becomes partly soluble. The portion 

 that dissolves is fluate of potash ; that which does not dis- 

 solve is siliceous fluate of potash. 



If, instead of making the experiment in a crucible, it be and in cxigefc 

 done in a small bent glass jar filled with oxigen gas, and 8 as * 

 heated gradually, the inflammation is more vivid than ia 

 common air, a great quantity of oxigen is absorbed, and 

 the gas that remains after the combustion is nothing but 

 pure oxigen, with the addition of a little fluoric acid. That 

 D » prodwet 



