170 INFLAMMABLE CAS FROM COALS. 



because a considerable portion of heat escapes through the 

 aperture C. 

 The cconomi- This apparatus may be used for different purposes ; such as 



cal use of the jjiat ofboilinff water at a small expence. It is of great utility 

 Jjresent appa- . .° , , . n- , 



ratus. "i domestic concerns. In order that its effect may be com- 



plete, the heated air ought to be deprived as much as possible 

 of its caloric. The author, or perhaps the editors of the 

 Journal des Mines, proceed to observe, that the cooled air 

 being heavier than that of the atmosphere, causes the current 

 in this kind of stove, and therefore they recommend that the 

 descending tube should be made as long as local convenience 

 inventors. will allow. It would not be needful to take notice of this over- 

 sight, if it were not accompanied with the practical deduction. 

 The current is, in fact, produced by the rarefaction of that part 

 of the air which ascends, and not by any increased density in 

 the descending part, which, by the condition of (he experi- 

 ment, ie, for the most part, in contact with hot water, and 

 never colder than the surrounding atmosphere. 



III. 



t-etier from il/r. Hume, of Long Acre, respecting the Carbu* 

 retted Hydrogen Gas procured from Ceals, by Z)r. Clayton, 

 early in the last Century. 



To Mr. NICHOLSON. 

 SIR, 



.S an addition to the information already before the public, 

 respecting the Hydrogen, or Carburetted Hydrogen Gas pro- 

 cured from Coals, it may not be improper to refer at once to 

 an authority, beyond all others the most authentic and easy of 

 access, I mean the Philosophical Transactions. In the 4 1st 

 Discovery°"of ^"'""^^ ^^ ^^^^ work, p. 59, there is a short paper on this sub- 

 the inflamma- ject, describing how the discovery originated, and some of the 

 Coals*^^^ ^^°'" elfects produced by this gas, or spirit of Coals. The paper 

 appears to have been read before the Royal Society, in Ja* 

 nuary, 1739, as, " a letter to the Hon. Robert Boyle, from 

 Chelate Rev. John Clayton, D. D.'* 



This 



