WRITINGS OF JAMES SMITHSON. 99 



mixture with which it melts, for the sake of promoting 

 division and multiplying surfaces. 



Hereby is supplied what may have seemed to be an omis- 

 sion in the paper on acids.* Although it was not such, since 

 fluorine is not an acid ; and fluoric acid may never occur 

 in a mineral substance ; as it can probably exist in combina- 

 tion only with ammonia ; all its other supposed compounds 

 being doubtless fluorides. 



2. The theory of these decompositions may be acquired 

 by experiment; and light obtained on the nature of the 

 compounds. 



If fluor spar, for instance, is a combination of oxide of 

 calcium and fluoric acid, and this is expelled from the oxide 

 merely by the force of fire, t{ie decomposition of it will take 

 place in closed vessels without the presence of oxygen or of 

 water ; fluoric acid will be obtained ; and the weight of this 

 acid and the lime will be equal together to that of the orig- 

 inal spar. 



If the spar is metallic calcium and fluorine, and when 

 heated in oxygen absorbs this, and parts with fluorine, it is 

 fluorine which will be collected in the vessels, and its weight 

 and that of the lime' will together exceed that of the spar 

 by the oxygen of the lime. 



If it is water which is the agent of decomposition, fluoric 

 acid will be collected ; but here the excess of weight will 

 not only equal the oxygen absorbed by the lime, but also 

 the hydrogen which has acidified the fluorine ; and this in- 

 creased weight of the fluoric acid will prove that hydrogen 

 is an element of it. 



It appears to have been fluoric acid which in the above 

 related experiments passed into the tubes ; but the inflam- 

 mable matter of the flame would probably have rendered 

 emitted fluorine such. It becomes of high importance to 

 ascertain whether ignited fluor spar is decomposed by pass- 

 ing water over it, and if so what are the products. It is 



* Annals for May. 



