Of Chimney Fireplaces, 5 1 5 



fire sufficiently forward, in altering a chimney con- 

 structed on the common principles, need never be 

 thicker than'the width of a common brick. I may say 

 the same of the thickness necessary to be given to the 

 new sides, or covings, of the chimney; or if the new 

 back and covings are constructed of stone, one inch and 

 three quarters, or two inches, in thickness, will be suffi- 

 cient. Care should be taken in building up these new 

 walls to unite the back to the covings in a solid manner. 



Whether the new back and covings are constructed 

 of stone, or built of bricks, the space between them 

 and the old back and covings of the chimney ought to 

 be filled up, to give greater solidity to the structure. 

 This may be done with loose rubbish, or pieces of 

 broken bricks, or stones, provided the work be strength- 

 ened by a few layers or courses of bricks laid in mortar; 

 but it will be indispensably necessary to finish the work, 

 where these new walls end, that is to say, at the top of 

 the throat of the chimney, where it ends abruptly in the 

 open canal of the chimney, by a horizontal course of 

 bricks well secured with mortar. This course of bricks 

 will be upon a level with the top of the doorway left for 

 the chimney-sweeper. 



From these descriptions it is clear, that, where the 

 throat of the chimney has an end, that is to say, where 

 it enters into the lower part of the open canal of the 

 chimney, there the three walls which form the two cov- 

 ings and the back of the fireplace all end abruptly. It 

 is of much importance that they should end in this 

 manner ; for were they to be sloped outward and raised 

 in such a manner as to swell out the upper extremity of 

 the throat of the chimney in the form of a trumpet, and 

 increase it by degrees to the size of the canal of the 



