12 ON THE LOSS OF HEAT 



ed, take a cylinder, or rather, an inverted conical frustum, of 

 cast iron, of any required thickness and diameter, and of suffi- 

 cient height to form the receptacle for the coal and ashes ; in- 

 sert a grate at a sufficient height from the bottom to leave the 

 required room for the ash pit, which should be provided with 

 a door to remove the ashes and unconsumed coal, as usual in 

 close stoves, and, also, to regulate the admission of air, which 

 may be heated as in those stoves. This cylinder may be 

 bricked in the ordinary manner on the outside ; and this can 

 be done with greater facility than for the grate, and the cylin- 

 der will remain more permanently fixed, as it will rest on the 

 hearth. From the satisfactory experiments which have been 

 made in double cylinder stoves, in which the interior cylinder 

 is made of cast iron, without any coating of clay, it is not 

 probable that this construction would require it. In those 

 instances in which beauty of construction must be consulted, 

 the ornamental parts or appendages to the open grates may 

 be added ; the only change suggested, being the substitution 

 of a cylinder, or other shape more desirable, of cast iron, in 

 place of the open grate. 



The particular requisites necessary to be attended to in the 

 construction of any apparatus intended for the combustion of 

 anthracite coal, in small quantities, having been sufficiently, 

 and, perhaps, tediously expatiated upon, those whose business 

 it is to construct, will apply any suggestions which may be 

 considered as valuable. 



Before closing my paper, I cannot forbear making a few 

 desultory remarks ; and, first, on the commonly received opi- 

 nion, that the " draught" of a chimney, or, more properly, the 

 current of air through it, has greater velocity under one degree, 

 of barometric pressure than another, and that this is the cause 

 why a combustible body burns better at one time than another. 



That the velocity of the current cannot be greater under 



one degree of atmospheric pressure than another, caeteris pori- 



, bus, may be satisfactorily shown, by supposing a room, with 



'one window open, in which is a fire-place and chimney, and. 



that the temperature of the air in the room, and that within the 



