AT FREIBERG. 



423 



necessary for the oxidation of the sulphurous acid. The main part of the process takes place in the two middle inter- 

 mediate chambers, and the roof chambers arc designed to condense the particles which have been mechanically car- 

 ried by the gases through the other chambers. The roast gases escape here through a chimney into the open air, the 

 greater part of the sulphurous acid having been converted into sulphuric acid. The gases that thus escape arc principally 

 brown vapors of hyponitric and nitrous acids, nitrogen and a small quantity of sulphurous acid, and some steam. 

 The steam necessary for the process is generated in a steam boiler outside of the lead chamber building, and is con- 

 ducted through a cast-iron pipe either through the sido or better through the roof of the lead chamber, and it inns' 

 have a certain tension on leaving the pipe in order that it may disseminate itself over the whole interior space. 



The nitric acid which is required in the production of sulphuric acid is made from Chili saltpetre and sulphuric 

 acid of 60° li. The decomposition of the saltpetre (nitre) takes place in close cast-iron retorts, underneath which is a 

 lire place and both ends of which are closed by movable iron doors. 2:10 lbs. of sulphuric acid and 250 lbs. of saltpetre 

 are put at one lime into a retort of this kind and this is repeated every two days. The nitric acid gas mixed with 

 peroxide of nitrogen is condensed in earthen jars (Woulfe's jars) containing water. 



From t centner of sal tpetre 1 50 lbs. of nitric acid are obtained, or 60 p. c. nitric acid of 86° B. This nitric acid which 

 condenses in the first jar has a strength of 40°-45° B., in the last jar about 15° B. The jars arc connected by earthen 

 nocks in the usual manner. 



As secondary produot of this part of the sulphuric acid manufacture are 3110-340 lbs. of sulphate of soda (Glauber 

 Salt). At the Muldner works there are throe such systems of load chambers, the first containing 94,000, the second 

 134,000, and the third 100,000 cubic feet. The lead chambers of the Halsbriickner Works enclose 159,000 cubic feet. 

 In Hie lead chambers the sulphuric acid is obtained as hydrated acid of 48° to 50" B., and containing a largo percentage 

 of arsonious acid. The acid collects in the bottom of the chamber, and must bo drawn off from time to time into a 

 basin provided for its reception. For greater facility in observing the strength of the acid, dropping apparatuses arc 

 introduced at different places on the sides of the lead chamber whore the newly formed acid, trickling down the 

 inside of the walls, is caught and allowed to drop into a little lead cup, from which it is again conducted 

 into the chamber by a leaden pipe. In this way it is easy to tost the strength Of the acid and thus to regulate the 

 amount of steam, nitric oxide, &c, which are to be admitted. The height of the acid in the chamber is ascertained 

 by means of glass tubes fastened into the sides like the float water-guagc of a steam boiler. If the acid in the 

 little cups shows a tendency to exceed 50^ B. in strength, either loss nitric oxide gas must bo admitted, or the amount 

 of steam increased. A system of lead chambers enclosing 94,000 cubic feet can produce daily 50-00 centners of 

 sulphuric acid of 60° B., and the consumption of nitric acid amounts to 5-6 centners in 24 hours. A system of 1(50,000 

 cubic feet can produce 100 cwt. of sulphuric acid of 66° I'.., with a consumption of nitric acid of 8-10 cwt. 



A normal run in this process is indicated partly by the warmth of the leaden walls (occasioned by the chemical 

 processes going on inside), partly from the regular and rapid dropping from the dropping apparatus into the leaden 

 cup before described, and lastly from the brown color of the gases which escape from the roof chambers. In order 

 to be able to observe the color of these gases more perfectly, two small glass windows are inserted into the opposite 

 sides of the chamber. 



II' flu- escaping gases are colorless or bright yellow it is an evidence that there is a lack of nitric oxide. 



The purification of the acid of the load chamber from arsonious acid is accomplished by means of sulphydric acid 

 which precipitates it as tersulphide of arsenic. The sulphydric acid is producod from a raw matt tree from zinc, 

 which is obtained by smelting lump-ore free from blende without roasting and with slag in a cupola furnace. 



This raw matt is broken into small pieces and treated with dilute sulphuric acid in a gas-llask with the assistance 

 of heat from steam which is conducted around the flask. To aid the wanning, these llasks arc surrounded by iron 

 jackets, The gas is led through a leaden pipe into a waste vessel partly filled with water, whoso use is firstly to 

 wash the sulphydric acid, and secondly to furnish a means of observing the course of the operation. 



The residue which remains in the gas-flask and which is very rich in silver is carried to the smelting furnace. 

 The solution of iron vitriol resulting from this production of sulphydric acid is evaporated to saturation, and then 

 transferred to crystallization tanks, and crystallized in the same manner as copper vitriol. The centner of Green 



