314 LECTURES TO SCIENCE TEACHERS. 



below, and the nitric acid fumes which are evolved pass 

 into a cast-iron pipe, which discharges its contents into the 

 long horizontal flue carrying the products from the pyrites 

 burners into the chamber. 



Here I may digress for a moment to remind you that the 

 enormous demands of the English sulphuric acid manufac- 

 ture has introduced industry and wealth into an arid dis- 

 trict in South America. In the rainless district of Atacama, 

 in Peru, a deposit of a white salt was discovered some years 

 ago, extending over an area of more than 200 square miles, 

 and of an average depth of several feet. This turned out to 

 consist chiefly of nitrate of soda, and it could be brought to 

 England at a cost of less than one-half of that of the 

 ordinary saltpetre or nitrate of potash. Many thousands 

 of tons of this material are now annually shipped from the 

 South Peruvian ports, and the greater part of this finds 

 its way into the nitre-pots of the English sulphuric acid 

 works. 



The existence of this comparatively new source of nitre 

 has given a fresh impulse to the manufacture of sulphuric 

 acid, rendering it independent of the high and varying price 

 of nitrate of potash. 



Before entering the chambers, the mixture of sulphur 

 dioxide, nitrous fumes, and air passes up a tower about forty- 

 five feet high, having an outside covering of strong sheet lead, 

 but lined inside with fire-brick, and having about fifteen feet 

 of its lower part filled up with pieces of flint. This tower is 

 closed at top and bottom, and the gases passing in by a 

 side flue near the bottom, issue by another side-flue near the 

 top of the tower. Above the closed top of the tower are 

 placed two reservoirs made of lead. One of these contains 

 strong sulphuric acid, which has been saturated with nitrous 

 fumes at a subsequent part of the process, whilst the other 

 is filled with a dilute- or chamber-acid, as it is termed, 

 because it is that which is drawn off the floor of the 

 chambers. By a very ingenious contrivance, given volumes 

 of the strong nitrated acid and the weak chamber-acid are 

 allowed to flow separately from these reservoirs down the 

 tower. Here the two acids meet, and the strong acid, 

 being thus diluted, gives up the nitrous fumes which it 

 formerly held in solution, and these are carried away with 

 the current of gases into the chamber. The downward 



