8 BULLETIN 283, TJ. S. DEPARTMENT OF AGRICULTURE. 



horizontally. Each layer of plates is supported, at some distance 

 above the other by bearers in such a way that every plate is inde- 

 pendent of the others. The plates are so constructed and placed 

 that the holes in those of one layer do not come directly above the 

 holes in the next layer below. 



Dilute sulphuric acid is allowed to trickle down the tower, splash- 

 ing from one layer of plates to another and meeting the hot-chamber 

 gases as they wind upward through the tower. The film of dilute 

 acid over the plates presents an immense cooling surface to the 

 gases and at the same time furnishes the water necessary for the 

 decomposition of the nitre-sulphuric acid. The formation of this 

 latter compound is, according to Lunge, a necessary link in the 

 chamber process. 



Gilchrist's pipe-column system * consists of lead towers (3 or 4 

 feet across and 15 feet high) having corrugated lead tubes, open at 

 both ends, running through them horizontally like a steam boiler. 

 The sides of the towers are boxed in with boards so as to form an air 

 shaft which terminates in a flue at the top. 



The chamber gases, together with water vapor, enter the pipe 

 columns at the sides near the bottom and work their way upward 

 through the towers. Contact with the air-cooled corrugated tubes 

 condenses the sulphuric acid, which then drips in showers from one 

 series of pipes to another and frees the oxides of nitrogen, restoring 

 them to the system. The gases issue from the top of the towers 

 and enter the next chamber, from which they are drawn into another 

 series of pipe columns, and so on through the system till their oxida- 

 tion is practically complete. 



While some of the methods just described are designed to cut 

 down the amount of chamber space required, none of them, with 

 the exception of Falding's process, reduces the initial cost of erecting 

 an acid plant; for, while less lead may be employed in constructing 

 the chambers, the expense of the cooling and mixing towers more 

 than offsets the saving in chamber material. 



Another objection to most of the accelerating devices discussed 

 above is that in order to mix the gases thoroughly they must bo 

 drawn or forced through small openings or made to pursue a mean- 

 dering course by means of baffles or some acid-proof packing material 

 in the towers. Under such conditions dust or impurities may clog 

 the apparatus, choking off the draft and making it necessary to 

 clean out the tower or chamber before operations can be resumed. 

 Moreover, the collapse or disarrangement of the packing material 

 within the tower may cause even more serious trouble. 



Nearly all modifications of tho chamber process complicate some- 

 what the running of an acid plant, and should therefore be constantly 

 under tho supervision of a competent chemical engineer. 



•Jour. Soc. Chem. Tn '., 1^. 15! 



