CLAYS OF NEW YOEK 



675 



close the opening; the frames are set in the courses of double-coal 

 brick, at the bottom of the arch on both sides of the kiln. Double- 

 coal brick have six or seven times as much coal dust in them as 

 others and are used for placing around the outside of the kilns. 

 The combustion of the coal in them, the manufacturer claims, sup- 

 plies the necessary amount of heat to the outer portion of the kilns 

 which are not sufficiently heated by the arch fires. Double-coal 

 bricks sell for about $2.50 a thousand, and usually bear some dis- 

 tinguishing stamp, but they are not as strong as the other brick. It 

 takes two setters and four wheelers about one day to set an arch of 

 35,0'00 brick; two men will daub the outside of a 15 arch kiln in 

 one day. 



Having " walled-up " the kiln with double-coal brick and daubed 

 it over, the next step is to start the fires and burn the bricks. The 

 principle of the process is essentially the same, whether wood, coal 

 or oil is used as fuel. 



First, every alternate brick of the " burnt platting " is stood on 

 end to allow the " water-smoke " or steam to escape as quickly as 

 possible. A fire is then started in the mouth of each arch. When 

 coal is used the fire is started on the windward side of the kiln so 

 as to allow the smoke to blow through the arches. 



The fire is also started from the other end of the arch, and the 

 two fires are then built up slowly till they meet in the middle. 

 The time of crossing the fires varies; with machine-made bricks 

 the fires should not be crossed as quickly as with handmade ones. 

 Along the Hudson the time of crossing is from 40 to 60 hours. 

 The steam should escape evenly all around the top, and the upper 

 limit of the fire should follow directly on it, the steam acting as 

 a blanket, and its lower limit should be even. It is the duty of 

 the foreman to watch the burning carefully, and increase or ease 

 up the steam in any one arch, according as it is coming off too 

 slowly or too rapidly. The fires are increased till the " water- 

 smoke " changes to a bluish black smoke, and at this point the 

 fire can be seen at night time coming from the top of the kiln. 



