THE KAOLIN FILTER 



123 



allows the water to trickle through san<l*ini\ and in that of 

 David it is forced in turn through layers of -wool treated 

 with iron tannate, sandstone, animal charcoal, and nrarcL 



The kaolin filters on the Chamherland-Pasteur principle 

 consist of porous tubes of porcelain (the so-called ' candles') 

 about 20 cm. long and 2 cm. thick, closed at one end and 

 provided at the other with enamelled points for the outflow. 



Supply-pipe connected with 



the metal 



Water 



Porcelain tube 



Enamelled discharge-pipe 

 FIG. 44. KAOLIN FILTER, ox THE CHAMBERLAXD-PASTEUK S^ - 



These are placed in the water to be filtered or fixed in metal 

 cases and screwed on to the supply-pipes ; several may 

 also be connected to form a battery (fig. 44). 



The micro-membrane filter of Breier consists of a fine 

 netting of metal covered with densely-packed asbestos, 

 which thus forms a thin filtering layer having excessively 

 fine pores. 



