The Phosphates of America. 99 



is full the cistern plug is reseated, and the screw-valve over the egg 

 firmly fixed in its place. 



The engine chosen for working the "egg" should have both a 

 steam and air cylinder, worked with a direct stroke, and should be 

 constructed to force acid through the delivery-pipe to the required 

 height with ease and freedom. 



The whole pumping-gear must be kept scrupulously clean and 

 in good repair, and it is a wise measure of precaution to provide 

 two " eggs " for each set of towers, so as to avoid, in case of a break- 

 down, any stoppage of the process. 



As the absorbing powers of concentrated sulphuric acid are 

 known to become less, proportionately, with the increase in its tem- 

 perature, the absolute necessity .for effectually cooling that which 

 runs from the Glover before passing it on to the Gay-Lussac tower 

 need hardly be insisted upon. 



A sufficiently long leaden worm pipe immersed in water, kept 

 constantly cold, will answer all purposes. 



The action which takes place in the deiiitrating column is ex- 

 tremely complicated. 



Briefly stated, it may be said that the gases from the furnaces 

 and the nitre-pots pass into and up the column at a temperature of 

 from 900 to 1000 F., being met and traversed in their course 

 by the fine down-pouring rain of acid proceeding from the two 

 cisterns placed over its summit. 



There thus simultaneously ensues a thorough denitration and 

 concentration ; the nitrous compounds given off by the acid from 

 the Gay-Lussac tower and the steam resulting from the evaporation 

 of the weak acid are both carried by the thoroughly cooled furnace 

 gases into the chamber, the acid flowing into the bottom cistern 

 being concentrated by the loss of its water to from 62 to 63 B. 



The proper position naturally indicated for a Glover tower, 

 therefore, is, as we have shown in our plan, as close a prox- 

 imity to the burners as may be compatible with perfect safety from 

 fire, since the hotter the gases, the greater will be the evaporation 

 and the higher the degree of concentration of the acid flowing 

 through it. 



Some ten years ago Mr. Scheurer-Kestner pointed out that 

 during the combustion of pyrites, there is formed in the furnace a 

 large quantity of sulphuric anhydride which, being carried into the 

 denitrator with the other gases, is presumably responsible, by its. 



