TECHNICAL CHEMISTRY. 315 



flow of acid acts in other respects beneficially. It cools 

 the gases, which come almost red-hot from the pyrites burn- 

 ers, and would melt the lead of the chambers if not cooled. 

 In this way a large quantity of water contained in the 

 dilute acid is evaporated, and goes into the chamber in 

 the form of steam, whilst the acid which falls to the 

 bottom of the tower has become concentrated, and therefore 

 more valuable. These denitrating towers are frequently 

 termed " Glover's towers," from the name of their in- 

 ventor; their use constitutes a very great step in the 

 manufacture, but to be effective they must be employed in 

 conjunction with another tower placed at the end of the 

 last chamber, and called the Gay-Lussac tower, the mode of 

 working of which I will explain to you shortly. 



Entering the first chamber (for usually two or three cham- 

 bers are worked in succession) at a height of eight, ten, or 

 even fifteen feet from the floor, and having a temperature of 

 dbout 75, the mixed gases meet with jets of steam intro- 

 duced at different parts of the chambers. In this first cham- 

 ber the largest quantity of sulphuric acid is deposited, falling 

 in drops on to the floor of the chamber, where it collects. 

 In order to test the working of the chambers, a tray of lead, 

 having an area of one square foot, and shown at (/), Fig. 5, 

 is placed in a slanting position inside, but near one of 

 the sides of the chamber, and a pipe is led from this 

 to the outside. The acid as it falls on this tray runs 

 out by the pipe, and thus the yield of one square foot 

 of the chamber is measured. Several of these gauges, 

 placed in different parts of the chamber, give the 

 average production. Passing through the first chamber, 

 which is often 90 or 100 feet long by 20 to 25 feet in 

 breadth and 16 to 17 feet in height, and has therefore a 

 capacity of somewhere about 40,000 cubic feet, the gases, 

 which have by no means deposited all their acid, pass 

 through a wide flue into the second chamber, where they 

 again meet with steam, and having traversed this, pass 

 again into the third, or exhaust, chamber, of the same size 

 as the other two. Here, if the process is properly worked, 

 all the sulphur dioxide is converted into sulphuric acid, so 

 that the gases issuing from this chamber ought to contain 

 no sulphur dioxide, but only air, aqueous vapour, and red 

 nitrous fumes. In order now to prevent the escape of these 



