224 



NEW YOKE STATE MCTSEUM 



in ]^ew York. Fireclays vary in color, being black, gray, red, 

 green, blue or white. Many are soft and can be dug with pick 

 and shovel while others are shale like in their nature and have to 

 be blasted, Fireware must be able to withstand great and 

 sudden changes of temperature. It should resist intense heat 

 without shrinkage or fusion, and it should also resist corrosion of 

 substances in a state of fusion. Coarsegrained ware resists 

 temperature while finegrained ware can best withstand corrosion. 

 If the fireclay is to be used for saggers it must make a product 

 which will not crack when subjected to repeated alternations of 

 heat and cold. The porosity of a fire brick is often caused by 



Molding-room of Gas-retort Works. 



coarse sand and may be remedied by the addition while prepar- 

 ing of ground burnt clay, or "cement clay" as it is called. 

 Ground quartz may be added if the material contains an excess 

 of alumina. Weathering the clay is of the utmost importance 

 and is often carried on for several months. It breaks up the 

 clay and tends to lessen shrinkage in burning. The clay is next 

 tempered as a further step toward the production of a homo- 

 geneous brick. It is first passed between rollers to break it up 

 and is further cut up in a ring pit ^together with sand. The 

 material is next soaked in a pit with water. , Several grades of clay 

 are usually mixed in certain proportions in this pit, the amounts 



