1818.] Mr. Gill on a Fumice Stone Table Furnace. 449 



contains ± of its weight of it. It had been for a long time 

 considered as an ore of tellurium. I made an analysis of a very 

 small quantity of it some years ago ; I could not find any tellu- 

 rium in it, but the blow-pipe always afterwards retained the 

 odour of this metal. During my researches on selenium, 1 

 recollected this circumstance ; and the friend who possessed 

 the mineral sent me a sufficient quantity for an exact analysis. 

 I find it to be composed of one atom of selenuret of silver, and 

 two of selenuret of copper 



Article XIV. 

 On a Fumice Stone Table Furnace. By Thomas Gill, Esq. 

 (To the Editors of the Annals of Philosophy.) 



No. 11, Covent Garden Chambers, 

 GENTLEMEN, May i4, 1818 



It is now upwards of ten years since it occurred to me that 

 pumice stone, being a volcanic glass and exceedingly light and 

 porous, might possess very sloiv conducting powers for heat and 

 cold, and consequently form an excellent support for fuel as a 

 table furnace ; and on trial I had the pleasure to find my conjec- 

 tures fully verified. I made hemi-spherical cavities of about an 

 inch and a half only in diameter in two small pieces of pumice 

 stone ; and after making side orifices into the hollow cavities 

 thus formed to introduce a blast of air, I filled them with 

 charcoal, putting in also a small piece of copper, and fitted them 

 together. On igniting the furnace and employing a pair of 

 common hand bellows, I soon raised the temperature of the fuel 

 to an extraordinary degree of vehemence, and found the copper 

 was completely fused with that very small quantity of fuel only. 



This success induced me to make another furnace of the same 

 material, but of a rather larger diameter ; though, possibly, the 

 smallest ever made to be useful, as it was merely a hemi-spherical 

 cavity of two inches and a half in diameter made in a piece of 

 pumice stone about three inches and a half square, and having 

 a channel on one side of it for the blast to enter ; and this has 

 continued in use with me nearly ever since as the basis of a 

 most convenient table furnace. 



Occasionally, however, I increased its capacity to hold fuel 

 by placing upon its flat top a ring formed of a narrow slip of 

 tinned iron, about one inch broad and 12 inches long, and 

 which could be coiled into a circle of greater or lesser diameter 

 according to the extent of surface 1 wished to give to the furnace, 

 and upon which I also occasionally laid a flat three-rayed sup- 

 porter, made of twisted iron wire, or of a metal plate, to hold a 

 vessel to be heated by the furnace. 



Vol. XL N° VI. 2 F 



