1824.] some Compounds of Fluorine. 105 



ever 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 element 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, arsenic- 

 ated nickel, 8cc. 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 inter- 

 nal 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 appara- 

 tus, represented above, I could not perceive a trace of it. A 

 more accurate observation of its fusion has shown me that it 

 does not, as generally supposed, form the cauliflower. It 

 appears to do so only where so large a mass is exposed to the fire 

 that but points of its surface are fused in succession. If a very 

 minute bit is employed, it is clearly seen to puff up like borax, 

 stilbite, &c. ; and then, like them, become less fusible; from the 

 separation, doubtless, of a vapourized element on which its 

 greater fusibility had depended. The smallest particle of fluor 

 spar shows no such inflation. 



We see here three several cases of intumescence in the fire : 

 one where a gas is absorbed ; one where a gas, or vapour, is 

 disengaged ; one where the two effects are concomitant. 



There may be persons who, measuring the importance of the 

 subject by the magnitude of the objects, will cast a supercilious 

 look on this discussion ; but the particle and the planet are sub- 

 ject to the same laws ; and what is learned upon the one will be 

 known of the other. 



Article V. 



On the Composition of the Ancient Ruby Glass, 

 By Mr. J. T. Cooper. 



(To the Editor of the Annals of Philosophy.) 



SIR, Jan. 11, 1824. 



The chief difference between the ancient and modern ruby 

 glass, I have understood from those who are in the habit of using 

 the latter in large quantities, consists in the hardness, or infusi- 



