The Phosphates of America. 137 



remembered, the most annoying failures will ensue at most incon- 

 venient seasons. 



Where such failures involve stoppages they are fatal to every 

 semblance of manufacturing economy, since every unnecessary 

 reduction in the day's dissolving tonnage, adds to the cost and 

 diminishes the profits. 



The wet scrubbers are packed with wood spars for two reasons: 

 First, because spars exert no thrust on the tower sides and so save 

 the necessity of tie-rods ; and, secondly, because they seem to afford 

 a maximum of interstitial, or scrubbing surface, to a minimum of 

 solidity. The fire-brick packing sometimes adopted is less eco- 

 nomical, for it not only largely augments the dead- weight of the 

 towers, but decreases the ratio of useful surface to solid material 

 by its pigeon-hole overlap. 



The spars are made of wedged section, in order to delay the 

 choking of the towers, both by affording extra space for the 

 deposit of silica, and by facilitating its detachment and convey- 

 ance to the tower base by the action of the water. Silica depos- 

 ited on the sides of square-sectioned spars, clogs the tower by 

 reducing the packing spaces, whereas on wedged-section spars, a 

 considerable deposit can take place without at all affecting the 

 packing-mesh. 



Where economy of water is an object one tall tower is prefer- 

 able to two or three shorter ones, but the best arrangement is a 

 tower of moderate height, divided into two packed upcasts, with a 

 downcast flue between 



