450 Mr. Gill on a Pumice Stone Table Furnace. [June, 



I next added another piece of pumice stone to the former one, 

 or basis, having a cylindrical hole through it of the same 

 diameter as the cavity in the furnace, which answered still more 

 completely ; and in this state it was very frequently seen in use 

 by Capt. Bagnold, who has lately introduced it into the labora- 

 tory of the Royal Institution, and given a short account of it in 

 the last number of " The Journal of Science and the Arts ; " but 

 without giving me the credit of the invention ! 



It has also been seen and adopted by other persons, as I very 

 much wished to bring it into use, being convinced that it would 

 form a most desirable instrument in chemical pursuits, as well 

 as in the arts. 



I have, however, since very materially improved the furnace, 

 having added to it another part in place of the last-mentioned 

 one. This consists of a piece of pumice stone about three inches 

 and a half square, having a conical perforation through it of 

 two inches in diameter in its smallest aperture, and three inches 

 and a quarter in its greatest ; this, when placed upon the basis 

 with its narrowest aperture uppermost and filled with charcoal, 

 after being ignited, will continue to burn for half an hour without 

 attendance, the charcoal continually falling down owing to the 

 widening form of the perforation, and will yield an equable heat 

 sufficient to keep a matrass or retort suspended over it, and 

 containing any aqueous liquid, not exceeding a pint measure, 

 constantly boiling during that time, when it may need a fresh 

 supply or fuel. 



It may thus be very frequently employed in place of a spirit 

 or Argandlamp; with an expense in fuel too small to deserve 

 estimation. 



If, however, the last-mentioned part of the furnace be placed 

 with its widest aperture uppermost, it will be capable of receiv- 

 ing into it and supporting the lower part of a Florence oil flask, 

 or other glass vessel of a similar size, and will keep such a quan- 

 tity of fluid in it as may be enclosed in the pumice stone, and 

 defended from cooling by the action of the air, constantly 

 boiling with no more fuel than can be contained in the lower 

 part of the furnace ; this is no doubt owing to its slow conducting 

 power for heat, the vessel being here posited in a similar manner 

 to a boiler set in brick-work. 



It will, perhaps, appear singular, that this furnace has no grate 

 nor apertures in its bottom to admit air ; it will, however, seem 

 more singular to assert, that it has no occasion for any ; no doubt 

 owing to the air finding its way through the side channel and 

 through the division between the two parts of the furnace ; and 

 still more especially to the very slow conducting powers for heat 

 of the pumice stone itself; and, indeed, unless the charcoal be 

 quenched after an operation is finished, it will inevitably consume 

 to ashes. I am, Gentlemen, your most obedient servant, 



Thomas Gill. 



