PRODUCTION OF SULPHURIC ACID. 53 
Theoretically this should prove the simplest, cheapest, and most 
efficient method of making sulphuric acid, but in actual practice 
there are several details encountered both in the construction and 
running of a plant which unless given careful consideration will 
seriously affect the yield of acid and the cost of production. 
Many different catalytic agents have been tried (notably platinum, 
palladium, iridium, the oxides or sulphates of iron, copper, chromium 
manganese, and silver, as well as the oxides of some of the rarer 
elements) in effecting the oxidation of sulphur dioxide, but no matter 
what catalyzer is used its efficiency is seriously impaired and often 
destroyed unless very elaborate systems are employed for purifying 
the gases before admitting them into the oxidation chamber. For 
instance, finely divided platinum (platinum black) has proved the 
most efficient catalyzer so far discovered, but the catalytic power 
of this body in bringing about the union of sulphur dioxide and air 
is seriously affected by the smallest traces of arsenic in the gaseous 
mixture. When pyrites are used as a source of sulphur dioxide, 
the arsenic which this mineral nearly always contains, passes over 
with the furnace gases and it is only by repeated washing and filter- 
ing that the last traces of this element can be removed. 
Contrary to general opinion, therefore, a contact plant is both 
elaborate and costly and strict supervision by a competent chemical 
engineer is necessary to insure the best results. 
The contact process has distinct advantages over the lead-chamber 
method where a pure concentrated acid is required, but in the manu- 
facture of ordinary sulphuric acid (50° to 60° B.) for the fertilizer 
industry or for other purposes where the purity of the product is 
not essential, the latter method still holds first place (at least in this 
country) for efficiency and low cost of production. 
THE LEAD-CHAMBER PROCESS. 
The lead-chamber process with its various modifications has been 
fully treated by Lunge.t. This author, as well as numerous other 
investigators, notably Weber, Winkler, Rascheg, Meyer, Pratt, Gil- 
christ, Falding, and Wedge, has described details of construction, 
methods of accelerating the chamber reactions, and proposed and 
discussed schemes for increasing the efficiency and lowering the cost 
of acid systems. It is thought, however, that a brief general descrip- 
tion of the chamber process will help toward a better understanding 
of the modification of the process proposed in this paper. } 
In this country nearly all of the sulphuric acid is made from 
pyrites. The lump ore is imported chiefly from Spain, while the 
“fines”? are a domestic product mined in Virginia, Georgia, Ten- 
nessee, and California. If the lump ore is used it is burned in brick 
1 Treatise on the Manufacture of Sulphuric Acid and Alkali, vol. 1. 
