AT ITiEIliEKG. 



425 



material from which these products arc derived, but besides those certain Purr and lead ores, very rich in sulphide of 

 arsenio, are treated directly for this metal. The process is carried on in furnaces closely resembling the English 

 Reverberating furnace with coke as the fuel. The furnace is connected with a very long condensation canal of brick 

 in -which the deposition of arsenious acid takes place. 



The arsenical dust is brought upon the hearth through two holes in the roof of the furnace in charges of 10 centners, 

 and is then spread out and submitted to a red heat. One workman has charge of such a furnace for 8 hours. 



The arsenious acid contained in the dust is sublimed by the high heat and passes from the furnace into the canal. 

 During the sublimation the workmen must continuously stir up and loosen the charge. In 24 hours 40-50 centners of 

 such dust are treated and the expenditure of fuel is 10 bushels of coke. 



The tine particles of ore contained in the dust remain upon the solo of the furnace either as powder or in a melted 

 condition, and as they are very rich in lead and contain some silver, they are taken back to the cupel furnaces and 

 mixed with the other argentiferous leads, form the charge Cor the lead process, but only when they have accumulated 

 lo such an extent as to leave no room on the hearth for a fresh charge, 



The roasting of the arsenical ores is conducted in a similar manner to the roasting of the pyritic ores in the 

 Reverberatory furnace. 



The dearsenized ore is again roasted. The dust which settles in the condensation canal isaiine white crystalline 

 powder. When several hundred centners of this powder have collected in the canal, the latter is cleaned out, the ar- 

 senious acid being packed in barrels made of strong staves and lined with paper. The centners is sold for 2,[- thalers 

 ($1.09). It is applied to the manufacture of pigments, and in che manufacture of glass, in dyeing, and lately in enor- 

 mous quantities in the preparation of aniline colors. That pari, of the arsenious acid which settles in the part of tho 

 canal nearest to the furnace is usually mixed to a certain extent with line particles of ore dust, which have boon me- 

 chanically carried along with it, and this is especially used in the fabrication of "White Glass" so called. This 

 "White Glass " is nothing more or less than melted arsenious acid. It is a homogenous mass translucent and slighty 

 yellow to milk white, with conchoidal fracture and strong vitreous lustre!. The manufacture of "White Glass" 

 is accomplished in small iron kettles which are placed over tin; lire place, their rims just reaching the level 

 of tho brick roof of the latter. Movable iron covers shaped like stove pipes and narrowing towards the 

 lop are placed over these kettles, and oonneot at their upper ends with the chimney. These covers are 3 

 to 4 feet in height and about 1| feet in diameter at the base. The Process depends upon the property of the arsen- 

 ious acid to sublime before it melts. Tho heat sublimes the arsenious acid which melts and settles on the hot walls 

 of these covers. When so much has collected there that the gases can no longer find egress to tho chimney, the 

 covers are taken off, and the " White Glass" knocked out of them and packed in kegs or barrels lined with paper. 

 Only a small portion of the arsenious acid escapes into the chimney. The impurities remain behind in the botttom 

 of the kettle. 



The least admixture of soot or sulphur causes rough and streaky glass. The sublimation point of arsenious acid 

 is somewhere about 230° 0. 



Manufacture of Red Giass. 



The ores containing arsenical and iron pyrites are used in the process. The percentage of arsenic varies from 

 1 to 1 3 p. e. 



The ore is distilled in clay retorts similar to those employed in the manufacture of illuminating gas. The sulphide 

 of arsenic sublimed by the lire of stone coal beneath the retorts, deposits in boxes of sheet iron inserted into the small 

 ends of the retorts, partly as powder and partly in a melted state. 



The residue winch remains in tho retort contains very little arsenic, but consists principally of a magnetio 

 sulphide of iron somewhat like magnetic pyrites. H is broken into small pieces, aaid delivered to the sulphuric acid 

 works to be used in making sulphuric acid. The arsenic collected in the iron boxes is a heterogeneous and variously 

 colored mass, possessing a, stony appearance on fresh surfaces of fracture. 



In order to convert the materia] into "Red Glass" it is first purified by melting it up in cast-iron kettles, and 

 AMER1. PHILOSO. SOC. — VOL. XIV — 10^ 



