104 Mr. Smithson on [Feb. 



that of topaz, it may be required to reduce it to fine powder, or 

 to act upon it by some admixture with which it melts, for the 

 sake of promoting division, and multiplying surfaces. 



Hereby is supplied what may have seemed to be an omission 

 in the paper on acids.* Although it was not such, siuce fluorine 

 is not an acid ; and fluoric acid may never occur in a mineral 

 substance ; as it can probably exist in combination 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, the 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 original 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 increased 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 inflammable 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 passing water over it, and if so what are 

 the products. It is not convenient to myself at present to make 

 the experiment : I therefore resign it to others. 



How far the difficulty which the action of fluorine on the ves- 

 sels in which it is contained, as opposed to its examination, 

 would be obviated by employing vessels of its compounds, as of 

 fluor spar, or of chloride of silver ; or whether it acts on all 

 oxides as it does on silica, experiments have not informed me. 



3. The vegetation of matters before the blowpipe is attributed 

 by a great chemist to " a new state of equilibrium induced by 

 heat between the constituent parts of bodies,"f but the pheno- 

 mena do not accord with the explanation. 



Was such the cause of the acquired infusibility, it would ma- 

 nifest itself through the whole mass as soon as fusion had 

 enabled the new arrangement. It is, on the contrary, confined 

 to the surface ; the interior portion continues fluid ; but where- 



• jlnnah for May. 



•f De l'Emploi du Chalumeau, p. 94. 



