SCEEENS PLATES EXPOSUKE 



209 



cells is the difficulty of cleansing them. Where a solution is 

 used which is liable to crystallise out such as bichromate of 

 potash the writer has had the side of such a cell forced 

 completely out by the mere force of crystallisation when the 

 solution has managed to get into the cemented joints, even 

 to a very slight extent. 



There are many other forms of trough on the market. 

 The one made by Messrs. Watson, and known as Kingsford's 

 trough (Fig. 66), is very convenient. Its construction is 



a b 



FIG. 66. Kingsford's Trough for Fluid Screens. (W. Watson & Son.) 



simple, consisting essentially of an outer circle of brass drawn 

 together at the top by means of a screw or screws. This brass 

 circle is lined with india-rubber, and has blocks of india-rubber 

 so placed as to keep in position the circular glass discs or faces. 

 The latter are gripped by the india-rubber when tension on 

 the outer metal band is increased by turning the screws, and 

 an absolutely water-tight fitting is the result. It also has the 

 advantage that by releasing the screws it can be taken to 

 pieces, either to be cleaned or to replace either of the broken 

 glasses, should this be necessary at any time. 



Any simple trough could be made by taking two plates of 



