232 FIRESIDE SCIENCE. 



are but few furnaces in use in this country which 

 do not allow of the escape of ashes into the air 

 flues ; and a more intolerable nuisance we are un- 

 acquainted with, unless it be the deleterious gases 

 which usually accompany the dust in the air cur- 

 rent. The injury to furniture, books, curtains, 

 paintings, etc., from this dust-impregnated air is 

 very great. In portable furnaces, besides the bad 

 joints connected with the interior parts, the outside 

 coverings and doors fit very imperfectly, and much 

 dust finds its way into the air passages from the 

 cellar or basement in which the furnace is placed. 



The results of the experiments undertaken prove 

 that the gaseous products of combustion do pass 

 through cast-iron under certain conditions. Some 

 portions of the cast-iron work of furnaces are more 

 readily permeable to gases than others. In manv 

 cases, the fire-pot is surmounted by a high dome, 

 cast in one piece. This forms the heat-radiating 

 portion. In casting this, the metal is turned into 

 the mould so as to bring the rim, or edge, fitting to 

 the fire-pot, uppermost; consequently, the crystal- 

 line structure is different, or less dense, at that por- 

 tion nearest the fire, and under the favorable in- 

 fluences of greater heat and less density this part 

 of the dome affords the easiest egress for the gases. 



It is impossible to construct furnaces or stoves 

 of cast-iron, and secure impermeability to gases. 



