536 Of Chimney Fireplaces. 



evident than that both of these fluids are forced or 

 pushed, and not drawn upwards. Smoke is frequently 

 said to be drawn up the chimney, and that a chimney 

 draws well or ill; but these are careless expressions, 

 and lead to very erroneous ideas respecting the cause of 

 the ascent of smoke, and consequently tend to prevent 

 the progress of improvements in the management of 

 fires. The experiment just mentioned with the coloured 

 water is very striking and beautiful, and it is well calcu- 

 lated to give a just idea of the cause of the ascent of 

 smoke. The cold water in the jar, which, in conse- 

 quence of its superior weight or density, forces the 

 heated and rarefied water in the bottle to give place to 

 it, and to move upwards out of its way, may represent 

 the cold air of the atmosphere, while the rising column 

 of coloured water will represent the column of smoke 

 which ascends from a fire. 



If smoke required a chimney to draw it upwards, 

 how happens it that smoke rises from a fire which is 

 made in the open air, where there is no chimney? 



If a tube, open at both ends, and of such a length 

 that its upper end be below the surface of the cold water 

 in the jar, be held vertically over the mouth of the 

 bottle which contains the hot coloured water, the hot 

 water will rise up through it, just as smoke rises in a 

 chimney. 



If the tube be previously heated before it is plunged 

 into the cold water, the ascent of the hot coloured water 

 will be facilitated and accelerated, in like manner as 

 smoke is known to rise with greater facility in a chimney 

 which is hot, than in one in which no fire has been made 

 for a long time. But in neither of these cases can it, 

 with any propriety, be said that the hot water is drawn 



