The Phosphates of America. 



color of the last chamber lessens or fades away, it is because of the 

 presence of sulphurous acid, which, if it were allowed to pass into 

 the absorbing tower, would not only denitrate the nitrous acid, 

 but would cause the dissipation of all the recoverable nitrogen 

 compounds. 



A sufficient attention to details which, if small in themselves, 

 are of the highest importance to the re- 

 sults, will bring a set of chambers in a very 

 short time to a state of perfect working 

 order, but it is positively essential that the 

 operations be presided over by a competent 

 superintendent, who, in addition to a fre- 

 quent examination of the furnace cinders 

 as a check upon the burning of the ores, 

 should also determine by a rough analysis 

 of the gases every day at their entry into, 

 as well as at their exit from, the chambers, 

 the approximate quantity of sulphurous acid 

 contained in the one case and the amount 

 of oxygen in the other. 



GAY-LUSSAC TOWERS. 



The solubility of nitrous acid in oil of 

 vitriol containing less than four molecules 

 of water was first taken advantage of by 

 the distinguished French chemist, Gay Lus- 

 sac, w r ho invented the columns which bear 

 his name, and with which even those who 

 still disdain their use are not unfamiliar. 

 The tower shown in the figure is a very prac- 

 tical form, and it must be built of eight - 

 pound sheet-lead and should be from 40 to- 

 50 feet in height, with an interior diameter 

 of from 5 to 6 feet, or such other dimensions 

 as are necessary to insure a cubical ca- 

 pacity of about two per cent, of the entire 

 chamber spaTse. 



Either a brick or a wooden framework 

 may serve as a support, but the foundation 

 must be solid and the tower itself kept 

 plumb and completely accessible to the air. 



