AT FREIBERG. 



421 



greatest care portions of it will adhere to the hearth sole, and these portions must be removed by an iron instrument 

 adapted to the purpose. Those agglutinated parts are stamped and again roasted for the oxidation of the enclosed 

 pieces of matt. The roasting is continued for 1 6 hours in charges of from 10-11 centners. The completely roasted matt 

 is drawn out of the furnaoe in Iron boxes, and transported to a mill where it is fust sifted, (lie line dust fed through 

 two sets of mill stones by which it is very finely pulverized, is again sifted and then placed In the dissolving tanks. 

 That portion of it which is too coarse to pass the sieves is stamped and roasted again in charges of 10 centners. The 

 solution is conducted in cylindrical vessels lined with sheet lead, and whose bottoms are made of antimonial lead. 



There are at present at the Ilalsbriicke smelting works two dissolving tanks, one great and one small one, the 

 former capable of holding I centners of finely pulverized roasted concentrated matt. About centners of acid of the lead 

 chamber (48° to 50° Bcaunie) are introduced into the larger of these vessels, and this is then diluted with twice the 

 bulk ofmothor liquor from previous operations. 



The mixture of acid and mother liquor is heated to the boiling point by the introduction of steam, and the roasted 

 and pulverized matt is then stirred in with wooden stirring-instruments in small quantities, while steam is steadily 

 admitted. In three-quarters of an hour the material is completely dissolved. The steam is now shut off, and the 

 liquid allowed to stand a quarter of an hour, in order that the finely divided argentiferous residue may settle, and the 

 saturated solution of 40 3 -42° Beaume clarify itself. In twenty- four hours, eight solutions are made in the larger 

 tank. After the liquid has cleared in the larger vessels, it is drawn oft 7 , by means of leaden syphons, into the crystal- 

 lization tank. Such a tank has a capacity of 100 cubic feet, and holds the liquor of four solutions. All these tanks 

 and vessels are lined with sheet lead. 



The argentiferous residue left in the dissolving tanks is well washed, in order to separate the copper vitriol, 

 then washed down through the cock, in the lower part of the tank, and just above the bottom, into a receptacle 

 beneath, where it is again well washed, and then filtered through linen cloth, and Anally dried in a furnace, and 

 conveyed to the Lead Process, to extract the silver. 



This residue consists in the main of sulphate of lead and metallic silver, particles of Sulphur, and anhydrous 

 salts of copper and iron. It averages :>>0 per cent, of lead, 2 to 2.5 per cent, of silver, and 7 to 8 per cent. 

 of copper. I n the crystallization tanks there are suspended numerous bands of lead, to which the crystals of sulphate 

 of copper attach themselves. Crystallization requires from eight: to ten days. 



These first crystals (raw vitriol), which, on account of the concentration of the solution, are somewhat unsightly 

 in their appearance, arc re-dissolvcd either in water or in mother-liquor, in other lead-lined tanks, heated, as 

 before, by steam. 



This liquor is crystallized in the same way, and produces the crystals of copper-vitriol which are required by 

 commerce. 



A portion of the mother-liquor which has only a strength of S5 ( Beaume" more or less, is used to dilute the 

 strong sulphuric add at- the commencement of vilriolization, while another portion is concentrated, by evaporation in 

 leaden pans, to the previous strength of 40-42° 15., and given over to crystallization. The vitriol crystals from this 

 part of the liquor are dissolved and crystallized again. The mother-liquor of this crystallization contains much iron, 

 besides all the constituents of the matt, of secondary importance, manganese, zinc, arsenic, and a considerable 

 amount of nickel ; and it is used to quench the red-hot ore from the roast furnaces. The mother-liquor of the 

 copper vitriol is used again and again to dilute the strong acid, as lias been said before, until it becomes so rich in 

 iron that it can no longer he used without rendering the copper crystals impure from that metal. 



The pure crystals of copper vitriol arc washed in water, to hv.o them from adhering aeid, then dried on long 

 shelves, in a room into which warm air is admitted, and dually packed in barrels and sold. 



The MANUK'ACTinuo ov SULPHURIC Acid. 

 I. Form and Composition of the Ores and Products rich in Sulphur which are adapted to this Process :— 

 There are applied to the production of sulphuric acid, 



AMEltl. PHILOSO. SOC. — VOL. XIV — 10G 



