224 O n th e Construction of Kitchen 



chimneys are of any considerable length, they cannot 

 fail to occasion a strong draught through them, which 

 will have a tendency to cause the cold air of the atmos- 

 phere to press in by every crevice between the brim of 

 the boiler and its cover; which streams of cold a'r, bjing 

 precipitated upon the surface of the boiling liquid, will 

 be there warmed, and then passing off rapidly by the 

 steam-chimney will occasion a very considerable loss of 

 heat. 



The rule for regulating the damper of the steam- 

 chimney of a boiler, whose cover is not steam-tight, is 

 this : close the damper just so much that closing it any 

 more would cause some steam to be driven out between 

 the joinings of the brim of the boiler and its cover. 

 When this is done, it is evident that little or no cold 

 air can enter the boiler by any small crevices in its 

 cover that may remain open, consequently little or no 

 heat will be carried off by the air of the atmosphere 

 from the surface of the hot liquid. 



I have been the more particular in explaining this 

 matter, as I am persuaded that a great deal of heat is 

 frequently lost in boiling and evaporating liquids, by 

 causing or permitting the cold air of the atmosphere to 

 come into contact with the surface of the hot liquid. 



Some, I know, are of opinion that a stream of fresh 

 air or a wind, which is made to pass over the surface 

 of a liquid that is evaporated by boiling, tends rather 

 to increase the evaporation than to diminish it ; but it 

 appears to me that there are strong reasons to conclude 

 that this opinion is erroneous. A very simple experi- 

 ment which I propose to make, and which others may 

 perhaps be induced to make before I can find leisure 

 to attend to it, will determine the fact 



