100 WRITINGS OF JAMES SMITUSON. 



notconvonient 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 

 vessels in which it is contained, as opposed to its examina- 

 tion, would be obviated by employing vessels of its com- 

 pounds, 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 blow-pipe is 

 attributed by a great chemist to a " new state of equilib- 

 rium induced by heat between the constituent parts of 

 bodies,"* but the phenomena do not accord with the expla- 

 nation. 



Was such the cause of the acquired infasibility, it would 

 manifest itself through the whole mass as soon as fusion had 

 enabled the new arrangement. It is, on the contrary con- 

 fined to the surface; the interior portion continues fluid; 

 but wherever any of this bursts the shell, and issues forth, 

 it is instantly fixed in immovable solidity; and when the 

 process has attained its final state, a hollow globule remains. 



Why is the change of quality limited to the surface ; how 

 has been produced the central cavity ; what has forced away 

 the matter which occupied it? A new clement has been 

 received from without, one which existed in the matter has 

 been parted with in a state of vapour. This double action 

 may probably be inferred wherever a matter presents this 

 species of vegetation. 



Some metallic bodies, as tin, lead, sulphuretted tin, arsen- 

 icatcd nickel, &c., present another species of vegetation, 

 caused by the absorption of oxygen, and the production 

 over their surface of a matter more bulky than the metal 

 from which it is produced, and infusible at the heat to 

 which it is exposed. Here no internal void forms. 



The mode of fusion of epidote had led me to suspect the 

 existence of fluorine in it ; but on trial with the second ap- 



* De I'Emploi du Chalumeau, p. 94. 



