and the Economy of Fuel. 37 



the pan of a certain thickness, 2, 3, or 4 inches, for 

 instance, and making all the air-holes point to one 

 common centre (to the focus or centre of the fire), this 

 furtive entrance of cold air into the fire-place will in a 

 great measure be prevented. 



This evil may likewise be prevented when circular 

 hollow iron grates are used, by narrowing the fire-place 

 immediately under the grate in the form of an in- 

 verted, truncated, hollow cone, the opening or diameter 

 of which above being equal to the internal diameter of 

 the circular rim of the grate, and that below (by which 

 the air rises to enter the fire-place) about one third of 

 that diameter. (See the Figure 5, Plate I.) This open- 

 ing below, through which the air rises, must be imme- 

 diately under the centre of the grate, and as near to it 

 as possible ; care must be taken, however, that a small 

 space be left between the outside or underside of the 

 iron bars which form the hollow grate and the inside 

 surface of this inverted hollow cone, in order that the 

 ashes may slide down into the ash-pit. 



As to the form and size of the ash-pit, these are mat- 

 ters of perfect indifference, provided, however, that it 

 be large enough to give a free passage to the air neces- 

 sary for feeding the fire, and that the only passage into 

 it by which air can enter is closed by a good door fur- 

 nished with a register. The necessity of being com- 

 pletely master of the passage by which the air enters 

 the fire-place has already been sufficiently explained. 



It is perhaps unnecessary for me to observe that, 

 where perforated earthen pans are used instead of iron 

 grates, the air-holes in the pans ought to be rather 

 smaller above than below, in order that they may not 

 be choked up by the small pieces of coal and the 



