into two portions--a furnace for burning the sulphur, and a chamber for
receiving the vapours. The system was thus developed into the one
followed at the present time. The sulphur, or, in most cases, cupreous
iron pyrites (a combination of iron and copper with sulphur), is burned
in specially constructed kilns or furnaces, and the hot gases,
consisting essentially of sulphur dioxide with the excess of air, pass
through flues in which are placed cast-iron "nitre pots" containing a
mixture of nitre (sodium nitrate) and vitriol. The gases thus become
mixed with nitrous fumes or gaseous oxides of nitrogen, and, after
cooling, are ready for mixing with steam or water spray in the lead
chambers in which the vitriol is produced. These oxides of nitrogen
enable the formation of sulphuric acid to take place more quickly by
playing the part of oxygen-carriers. Sulphuric acid is formed by the
union of oxygen with sulphur dioxide and water; the oxides of nitrogen
combine with the oxygen of the air present in the chambers, then give up
this oxygen to the sulphur dioxide and water or steam to form sulphuric
acid, again combine with more oxygen, and so on. The exact processes or
reactions are of course much more complicated, but the above represents
what is practically the ultimate result. It is evident that the gases
leaving the last lead chamber in which the formation of vitriol is
effected, must still contain nitrous fumes, and it becomes a matter of
importance to recover them, so that they can be used over again. To
effect this object, use is made of the solubility of nitrous fumes in
strong vitriol. The gases from the last lead chamber of the series are
passed through what is called a Gay-Lussac tower (the process was
invented by the eminent French chemist Gay-Lussac), which is a tower
made of lead, supported by a wooden framework, and filled with coke or
special stoneware packing, over which strong vitriol is caused to flow.
The vitriol dissolves the nitrogen oxides, and so-called "nitrous
vitriol" flows out at the base of the tower. The recovery of the