78 MODERN HIGH FARMING. 



Our own opinion is that those which are 125 to 150 feet long, 20 

 to 25 feet wide, and from 12 to 15 feet high, best answer the require- 

 ments it being necessary to have them large for very important 

 reasons ; first, because of the bulk of the gases which enter, and the 

 necessity for their coming into direct contact ; and, second, because 

 the air only contains in every hundred, 21 volumes of available oxygen. 



Upon meeting with the steam, the sulphurous vapors combine 

 with certain portions of its hydrogen and oxygen, and immediately 

 become a liquid and tangible body known as sulphuric acid, while 

 the nitric acid vapors, casting off all their hydrogen, unite with the 

 oxygen of the air and become nitric peroxide. 



The sulphuric acid falls to the floor of the chamber, and the ni- 

 tric peroxide passes out at the end opposite to that by which it en- 

 tered, and is conducted into absorbing columns known as "Gay 

 Lussac" towers, where it is absorbed in concentrated sulphuric 

 acid, and, conducted by a complicated process back to the regions 

 of the nitre pots, where it assumes its original form, and thus 

 is continually utilized over again. 



It is on the good and careful, or faulty working of this pro- 

 cess of denitration that depends the saving or the loss in the consump- 

 tion of nitrate of soda to which we have already alluded in a former 

 chapter, and it has ever been the greatest difficulty with which chem- 

 ists have had to deal. Without dwelling upon the various old-fash- 

 ioned methods still in use in many factories, we will endeavor to give 

 a rough outline of that which is now generally looked upon as 

 most successful. 



The "Gay -Lussac" columns, to which we have alluded, are 

 named after the distinguished French chemist who invented them 

 some forty years ago, and are high and narrow leaden towers packed 

 with small lumps of coke and supported on a framework of timber. 



The nitric peroxide and the other vapors which issue 

 from the chambers are led into these towers through openings 

 at the bottom, and are met in their ascent by a current of concen- 

 trated sulphuric acid, flowing in a small stream from a cistern placed 

 over each tower and pumped up thither by a small forcing engine. 



