424 



SMELTING PROCESSES 



vitriol brings one Thaler 10 neugroschen "(one dollar). Tlio sulpbydrio acid gas pours out into the precipitation 

 tower, a large cylindric structure lined with sheet lead, which it entirely fills. Over this precipitation tower is a 



reservoir containing Hie still impure acid of the lead chamber which is allowed to trickle into the tower through 

 openings in the bottom of the reservoir. As the acid enters it becomes saturated with the sulphurated hydrogen and 

 the arsenic is precipitated in the form of a yellow mud. The sulphuric acid along with this arsenic mud runs into 

 vats at the bottom of the tower and is allowed to stand till the latter lias almost entirely settled, when the former is 

 pumped up again into the reservoir, and again allowed to trickle down the sides of flic tower, till a portion in a beaker 

 glass shows little or no arsenic after being saturated with sulphydric acid and allowed to stand for some time. A 

 pumping apparatus is used to carry the purified sulphuric acid from the vats at the bottom to the reservoir on the; top 

 of Hie tower. Tt consists of a small steam engine with horizontal cylinder, which moves the piston in an air 

 cylinder, compressing the air through tubing in an air fight vat into which the acid lias been previously run. 



The tcrsulphidc of arsenic is permitted to settle as perfectly as possible in lead-lined wooden tanks, the acid being 

 decanted off as completely and clearly as possible by leaden syphons and run into the evaporation pans. 



The yellow arsenic mud is washed thoroughly with water to get lid of the sulphuric acid. This is done in filtering 

 vats lined with lead and provided wit li numerous apertures in the bottom by which the wastewater can escape. 

 The purified arsenical precipitate is taken out to the drying hearth, where it is freed of its water and transferred to the 

 arsenic works for further treatment. 



Evaporation of the purified sulphuric acid. This is undertaken in leaden pans, of which there arc four on the 

 same level or in terrace form one above the other. The pans must be very shallow to facilitate the evaporation, and 

 the acid must not be more than 13 to 15 inches deep in any part of the vessel. 



The degree of concentration to which the sulphuric acid is brought, in this operation is exactly 60° B. A stronger 

 acid would attach the lead at that temperature. 



The foremost, pan in which is the acid of 60° 13. rests directly on the iron plates over tho fire place. The acid to 

 be concentrated is transferred from one pan to the other towards the fire, so that the last pan into which it comes is 

 directly over the fire place, while thelirst one filled is furthest from the lire. 



The steam from the evaporation, strongly impregnated with acid, escapes into the open air through a, long hood 

 connecting with a chimney which is so arranged as to hang directly over the pans. 



Stone coal is used as a fuel for the evaporation. This process is continuous, i. c, as much acid is let into the 

 hindmost pan to be concentrated as of tho 60° 13. acid is taken out of the pan over the lire place. The further con- 

 centration of the 00° 13. is undertaken in a platina retort of several cubic feet contents. Tho 60° Ik acid is boiled in 

 this platina retort,, and the strong acid vapor conducted through an aperture in the platina cover through a helix 

 which rests in a vessel tilled with cold water, ami into a receptacle under the end of the helix for the collection of the 

 condensed vapor. This is removed to the evaporation pans, and again concentrated witli the rest. Tho sulphuric 

 acid of (>(>' ' I!, strength being specifically heavier than the weaker acid, sinks to the bottom of the retort, whence it 

 is removed by means of a platina, syphon. This acid is run into glazed earthen ware pitchers and tilled from these 

 into carboys. 



It is ()(i' J I!, perfectly colorless and transparent and oily, has specific gravity 1.84, and is tolerably pure hydrate 

 of sulphuric acid From decomposition of the little organic materials of which the air is always more or less full, it 

 gets very often a brown color. The carboys are covered with willow withes, and are each packed i n a, box with straw, 

 the neck just protruding a little above the lid. After being filled they arc closed by earthen wan; stoppers, and sealed 

 with melted sulphur and sand. 



The centner of sulphuric acid of (i(i 13. is worth 2 thalcrs ($1.50), exclusive of the packing and carboy which costs 

 2 i iii-ii groehen (07 cts.). Some (10 > 13. acid is sold also at 1 thaler 12 n. gr. ($1.05). The cut. of unpurified sulphuric 

 acid of 60' 15. is sold for I thaler 21 n. gr. (81 cts). This is now extensively used to decompose the phosphates in tho 

 superphosphate manufactories. 



Tin.; Manufacture of Various Arsenical Articles of Commerce. 



The arsenic works are employed in the production of arsenious acid, metallic arsenic, and various sulphides of 

 arsenic. The arsenical dust from the condensation chambers of the Koasting Furnaces furnishes the most of the 



