CLAYS OF NEW YOEK 



6Y3 



on the nature of the clay used and the grade of product desired. 

 Common bricks for instance may not require a temperature of more 

 than 1800° F., while other wares may have to be burned at a tem- 

 perature of 2300° F. or 2500° F. 



In the burning process a number of different things exert more 

 or less influence and consequently must be taken into consideration. 

 Among these we may mention the character of the clay, the char- 

 acter of the fuel, the type of kiln to be used, the temperature em- 

 ployed, the composition of the fire gases, etc. 



The detailed changes which the clay undergoes, when burned 

 have already been mentioned. 



In burning, the wares are piled up in the kiln, as in the case of 

 common brick, and front brick, or they may have to be inclosed 

 in receptacles to protect them from the action of fire gases, and 

 they may sometimes need to be partially inclosied by means of fire 

 brick slabs in order to prevent the exertion of any excessive pressure 

 on them, which would cause them to lose their form. 



Some clays are burned only to a condition of incipient fusion, 

 while others are burned to a stage of vitrification. Common brick 

 are an example of the former, paving brick of the latter. 



The type of kiln used varies with the product and also with the 

 locality, but in every case it is either up-draft or down-draft. 

 In the former case the. fire passes from the bottom of the kiln up- 

 ward through the ware and out at the top, escaping either at many 

 points or through a chimney. In the latter case the fire is con- 

 ducted to the top of the kiln first by means of " pockets " or " bags " 

 on the interior wall, passes downward through the ware and then 

 out through flues in the floor of the kiln to the stack. All kilns 

 are also either continuous or intermittent in their action. In the 

 former the heat from the cooling chamber is conducted through 

 those which have not yet been burned, and is used to heat them 

 up. Both the up-draft and down-draft kilns are either rect- 

 angular or round in form, the former having a larger capacity. 

 The different types of kiln are mentioned in more detail farther on. 



