672 NEW YOEK STATE MUSEUM 



specially if a continuous one is used. This method works best 

 where the kiln is placed in the lower story of the factory, while the 

 molding machine is on the second floor, or in other words on the 

 same level as the top of the kiln. The bricks when molded are 

 set on the cars, and wheeled directly to the pallet racks. When 

 dry, they are loaded on barrows or cars, and sent down to the kiln 

 on an elevator. The one disadvantage in this method lies in the 

 extra handling of the bricks. The cost of the drying tunnel is 

 however done away with. 



Burning 



In the burning of clay, the chemically combined water and also 

 any carbonic acid which may be present are driven off, while the 

 organic materials contained in the clay are also burned. As a re- 

 sult of this, the clay loses more or less weight, which in calcareous 

 clays may be as much as 20/^, and the porosity increases as a rule 

 with the amount of loss on ignition; but, if the temperature is ele- 

 vated enough to soften any of the clay particles, the various grains 

 of the mass will draw together, more or less, and the porosity will 

 be diminished. The hardness of the material will also be increased, 

 and this is specially true of calcareous clays. In the case of com- 

 mon brick it is always the finest particles of the clay that soften 

 when a temperature of about 1000° F. is reached, but the small 

 particles of quartz sand do not soften, and therefore form the skele- 

 ton of the mass, thus enabling the brick to hold its form. As at this 

 temperature the quartz sand expands as much as 16^, and conse- 

 quently decreases in specific gravity, there will be a certain amount 

 of decrease in the porosity from this cause. We therefore can 

 obtain thoroughly dense brick from sandy clays, without the burn- 

 ing process being accompanied by any material amount of shrink- 

 age, the quartz having aided in rendering the clays more dense. 



In the burning the clay changes from a comparatively soft con- 

 dition to one of rock-like hardness. The amount of heat applied 

 in burning and the temper? ture to which the kiln is raised depend 



