OXIDES AND OXYGEN ACIDS OF SULPHUR 



267 



all the necessary constituents, excepting water, the gases next 

 enter the first of the lead chambers, large structures lined com- 

 pletely with sheet lead. These measure as much as 100 X 40 X 

 40 feet, and have a total capacity of 150,000 to 200,000 cubic 

 feet. As the gases drift through these chambers they are thor- 



FIG. 71 



oughly mixed, and an amount of water considerably in excess 

 of that actually required is injected in the form of steam at various 

 points. The acid, along with the excess of water, condenses and 

 collects upon the floor of the chamber, while the unused gases, 

 chiefly nitrous anhydride and nitrogen, the latter derived from 

 the air originally admitted, find an exit into the Gay-Lussac 

 tower L. 



This is a tower about fifty feet in height, filled with tiles, over 

 which concentrated sulphuric acid continually trickles. The 

 object of this tower, to catch the nitrous anhydride and enable it 

 to be reemployed in the process, is accomplished by a reversal of 

 action (2) above. The acid which accumulates in the vessel at 

 the bottom of this tower contains, therefore, nitrosylsulphuric 



