422 Dr. Clarke upon the Gas Blotvpipe, [June,* 



lustre ought to equal that which is presented after filing the end 

 of a piece oiiron wire, or the experiment has failed. 



It nas always failed when the fused barytes leaves traces of a 

 white powder upon the file. 



It has, moreover, always failed when the fused mass exhibits 

 the slightest degree of translucency ; or is of a grey, greenish, 

 or white colour. 



It has always failed when the experiment has been protracted 

 beyond the point at which the metal begins to burn, and is dissi- 

 pated in white fumes. 



To all those gentlemen who have so often witnessed the per- 

 fect metallic appearance of the melted harytes in my lecture 

 room at Cambridge, I may now appeal for the trutn of the 

 result ; being veiy anxious that others should also witness the 

 same appearance, to whose testimony it may never be in my 

 power to appeal. It would be to no purpose enumerating 

 the names of those who have been present with me during my 

 experiments ; persons not only of this University, but from 

 various parts of the kingdom, visiting Cambridge, have satisfied 

 themselves in this respect. Vipon April 'iO, 1819, there were 

 present for this purpose from London, Mr. W. Hamilton, Under 

 Secretary of State ; our Envoy to Constantinople ; Mr. B. Prere; 

 liis brother Mr. Serjeant Frere, Master of Downing College; 

 Jlr. Meyer, Consul at Corfu ; Mr. Mackenzie, of the Foreign 

 Ofl&ce ; and also Colonel Leakes, of the Artillery ; all of whom, 

 independently of those whose residence here gives them more 

 frequent opportunities of being present at these experiments, 

 are able to vouch for the truth of the statement 1 have made. 



But so lately as the 25th of April, of the present year, Prof^ 

 Muller, of Copenhagen, together with several gentlemen of this 

 University, were present at a series of experiments conducted 

 with the gas blowpipe, and all of them witnessed the revival of 

 the metal of barytes by means of this instrument. The experi- 

 ment was conducted as before described ; and was repeated in 

 their presence always with the same result. Prof, Muller took 

 away with him a specimen of the metal so revived ; but which 

 of course would speedily afterwards be again converted into the 

 state of an oxide. It is sufficient, however, to observe, that 

 they all saw it in the metaUic state. If, therefore, the experi- 

 ments elsewhere should not be attended with the same results, 

 the circumstance must admit of this obvious inference ; that the 

 means resorted to, and the manner of using the instrument, 

 have not been made adequate to the end proposed, which other- 

 wise might have been accomplished. 



The other chemical changes which bodies undergo when 

 exposed to the full powers of the gas blowpipe, and which 

 appear to me to be of a nature sufficiently remarkable to merit 

 ^e attention of chemists, are as follow : 



