BRICK YARDS 



227 



are made by means of a core attached to the end of the die, the 

 bending of the pipe being caused by the core forcing the clay out 

 through the die faster on one side than the other. Underneath 

 the end of the cylinder is a counterpoised table which receives 

 the pipe as it issues. When a sufficient length of pipe has issued 

 the press is stopped and the pipe cut off at the mouth of the die. 

 It is then removed from the table, which, relieved from the 

 weight, ascends to receive another length of pipe. Y joints are 

 made by hand, a hole being cut in the side of one piece of pipe 

 and the end of another trimmed to fit over it, the joint being 

 closed by means of wet clay. 



After the pipes are molded they are set on the drying floors 

 until thoroughly dry. Burning is done in circular down draft 

 kilos, such as those described in the manufacture of brick. It 

 takes five to eight days. The glaze to sewer pipe is made by 

 adding salt to the fires toward the end of the burning and when 

 the fires are hottest. The salt is thrown into the fireplace and 

 by the heat is broken up into hydrochloric acid and oxide of 

 sodium, and this latter fluxes with the silica in the pipe forming 

 a vitreous coating known as the " salt-glaze." When sewer 

 pipes are made of pipe clay, they are often coated with " Albany 

 Slip," a calcareous clay obtained in the Hudson River Yalley. 

 The material composing this fuses at a lower temperature than 

 the fire clay and gives the desired glaze. The composition of this 

 material published in Yol. YII of Ohio Geol. Surv. 1 893 is : 



Silica 60 . 59 



Alumina 12.46 



Oxide of iron 5. 79 



Lime 6.84 



Magnesia 3 . 28 



Alkalies 4.39 



Water 5 . 82 



99.17 



Another analysis given in the Clay-worker of December, 1 894 : 



Silica 58.47 



Alumina 16. 9^ 



Lime 6.19 



Magnesia Ti\ 



