132 CHEMICAL FERTILIZERS 



necessary amount of water. If the acid were allowed to 

 become too strong, other reactions would take place, and 

 certain amounts of nitrous oxide might be evolved. As a 

 rule, the temperatures in most works in Great Britain are 

 not sufficiently high to permit the use of water sprays in 

 place of steam, but in countries where temperatures are 

 higher, the use of steam only is found to give too high a 

 temperature. Generally, the acid produced in the last of 

 the leaden chambers is small in amount and weak in strength, 

 and is of no use for the* direct manufacture of artificial 

 manures. It is very common to find that the works where 

 superphosphate is made have some small side manufacture 

 where this weak acid can be utilized. Where this is not the 

 case, the weak acid must be concentrated. After leaving 

 the leaden chambers, the gases then pass up through the 

 Gay l,ussac tower, down which strong sulphuric acid trickles. 

 This acid is cold, and has a specific gravity of about 175. 

 Partly owing to its high strength, and partly owing to its 

 low temperature, nitric oxide is absorbed by the sulphuric 

 acid. The nitrified acid so obtained is sent away to the Glover 

 tower, where, owing to the dilution by chamber acid and the 

 high temperature of the gases produced from the pyrites 

 burners, nitric oxide is again given up. Owing to its low 

 temperature, the Gay Lussac tower may be safely filled 

 with coke, but the Glover tower is generally packed with 

 acid-resisting bricks. The temperature of the gas entering 

 the Glover tower is about 3OO-400 C. (57o-75o F.), 

 but when entering the leaden chambers it is reduced to 

 about 5o-8o C. (i2O-i8o F.). The acid leaving the 

 Glover tower has usually a specific gravity of 1-53 to 

 i '62. In the Glover tower the gravity of the acid may 

 be raised to 17, with 79 % of pure acid; a higher 

 strength cannot be obtained, as it would then begin to 

 absorb nitrogen oxides. For fertilizer purposes it is not 

 desirable to produce strong acids, and a gravity of i'6 is 

 usually aimed at. 



" Reinforced lead " is made by coating iron wire with 

 lead and embedding it in sheet lead. " Reinforced lead " 



