and the Mode of its Communication. 127 



broad and shallow vessels (flats), in which brewers cool 

 their wort, of metal, on a supposition that the process 

 of cooling would go on faster in a metallic vessel than 

 in a wooden vessel ; but this would not be found to be 

 the case in fact, a metallic surface being ill calculated 

 for expediting the emission of calorific rays. 



The great thickness of the timber of which brewers' 

 flats are commonly made is a circumstance very favour- 

 able to a speedy cooling of the wort ; for, when the flats 

 are empty, this mass of wet wood is much cooled, not 

 only by the cold air which passes over it, but also and 

 more especially by evaporation ; and when the flat is 

 again filled with hot wort a great part of the heat of 

 that liquid is absorbed by the cold wood. 



In all cases where metallic tubes filled with steam are 

 used for warming rooms or for heating drying-rooms, 

 the external surface of those tubes should be painted or 

 covered with some substance which facilitates the emis- 

 sion of calorific rays. A covering of thin paper will 

 answer that purpose very well, especially if it be black, 

 and if it be closely and firmly attached to the surface of 

 the metal with glue. 



Tubes which are designed for conveying hot steam 

 from one place to another should either be well cov- 

 ered up with warm covering or should be kept clean 

 and bright. It would, I am persuaded, .be worth while, 

 in many cases, to gild them, or at least to cover them 

 with what is called gilt paper, or with tin foil, or some 

 other metallic substance which does not easily tarnish 

 in the air. 



The cylinders and principal steam-tubes of steam- 

 engines might be covered first with some warm cloth- 

 ing, and then with thin sheet brass kept clean and 



