1821.] X)r. Clarke upon the Gas Blowpipe. 42$ 



1. Rock crystaly or any other highly refractory siliceous or 

 aluminous substance, beins^ allowed to fall upon a deal board, 

 while in fusion, and there left to become cool, exhibits upon the 

 surface that came into contact with the wood, where it forms a 

 charcoal cavity, a metallic lustre, equal to that of polished 

 silver. This metallic appearance may be preserved for any 

 length of time unaltered. Some of the students in this Univer- 

 sity have preserved specimens of melted rock crystal thus 

 invested by a seeming metallic body, the nature of which is 

 unknown. 



2. White opaque quartz melted in the flame of the gas blowpipe 

 becomes so highly limpid and transparent, that after fusion it 

 has all the appearance of rock crystal. The Plutonists may, 

 perhaps, hence infer, that the transparency of rock crystal is; 

 owing to the heat it has sustained. 



3. The varied and striking colours of metallic oxides arp 

 surprizingly developed by the flame of this blowpipe. Among 

 these, one of the most striking from its beauty is the intense red, 

 or bright purple, colour of the oxide of calcium, as displayed 

 during the fusion of Iceland spar. It is a colour which cannot 

 easily be described ; being much more vivid and striking than 

 the colour which the oxide of strontium communicates to the 

 same flame, and of a hveUer hue. Add also the beautiful rosy 

 colour of the oxide of gold, after its combustion upon pipe-clay 9 

 the deeper purple hue of the compound oxides oj gold and tin, 

 when the alloy obtained from the precipitate of cassius has simi^ 

 larly sustained combustion, the green colour of the oxide ofrho-^ 

 dium, &c. &c. 



4. The gaseous fluid which escapes during the fusion of pure 

 silica, has never been collected, and, of course, remains unknown. 



5. The dark powder dispersed during the combustion of plati- 

 num requires further examination. From some experiment^ 

 made with this substance, of which I before pubhshed an 

 account,* it seems to be the protoxide of the metal. 



6. The dark sooty-looking powder that remains after the solu- 

 tion of crude platina in nitromuriatic acid, divested of all metal- 

 lic particles which may remain undissolved, and consisting 

 essentially of the oxides of iridium and osmium, is one of the 

 most refractory substances that have been exposed to the gas 

 blowpipe. By making a filter which was invested with this 

 powder into a pellet, and exposing it upon charcoal to the full 

 power of the flame, I succeeded in melting it into a brittle 

 metallic mass mixed with a deep blue glass, which had resulted 

 from the silicated alkali contained in the paper of the filter, as 

 in all vegetable bodies. It was not rendered malleable. The 

 surface of the charcoal during this experiment was covered with 

 an oxide of a dark Ulac purple hue. 



, * See Annals of Fhilos&phy. 



