METALLURGY. 



Assay. 



Manga- 

 nete. 



In Spain the cinnabar is collected and divided into 

 three portions. 



1st, The richest part of the ore. 



2d, That which contains less metal. 



3d, The powder of the two first. 



These are exposed to heat in a furnace, by which 

 the mercury is expelled. The furnace employed in 

 this operation is of a particular construction. It con- 

 sists of a long horizontal building, divided into an un- 

 der and an upper compartment, by a grating of iron. 

 On this are placed flat rough stones, over which ore 

 No. 2. is first put, and then ore No. 1. A layer of 

 ore No. 2. is placed above this ; and on the top of the 

 whole is laid ore No. 3. made into a sort of bricks, 

 with clay kneaded and dried. Wood is then kindled 

 in the lower compartment of the furnace, by which the 

 moisture is driven off. The fire is then continued till 

 the sulphur begins to burn ; after which the heat ex- 

 cited by the combustion of the sulphur, is sufficient to 

 volatilize the mercury, which is condensed in the re- 

 ceiver attached to the furnace. Along with the mer- 

 cury there is collected a quantity of sooty matter, which 

 is removed by placing the metal on an inclined table. 



In this process there is a considerable loss of mer- 

 cury, as the sooty matter which is thrown away re- 

 tains a great deal of the metal. 



In Germany, the finer part of the ore is separated 

 from the coarser part, and is reduced to powder. It 

 is then mixed with about one-fifth of slaked lime, and 

 put into iron retorts, each of which holds about one- 

 half cwt. From 40 to 50 of these are built into a fur- 

 nace, and have receivers adapted to them. Heat is 

 applied to the retorts, by which watery vapour is 

 at first expelled. The receivers are then luted by 

 means of clay, and the mercury which comes over is 

 condensed in them. By this process 100 Ibs. of ore 

 yield from 6 to 10 oz. of mercury. 



Assay. The assay of the ore of mercury is very simple. 

 Cinnabar, the ore usually employed for yielding the 

 metal, is reduced to powder, and digested in nitro- 

 muriatic acid, composed of one of nitric, and three of 

 muriatic acid diluted with water, till the whole of the 

 soluble matter is extracted. Carbonate of potassa is 

 then added to the solution, and the precipitate, after 

 being dried, is mixed with lamp-black, and exposed 

 to heat in a retort, to which a receiver is adapted. By 

 this means the mercury is expelled in the metallic 

 state. 



The ores of mercury which contain silver are as- 

 sayed in the same way, so as to ascertain the quan- 

 tity of mercury. The insoluble residue is then roast- 

 ed, to drive off the sulphur, after which it is mixed 

 with twice its weight of pearl-ashes, and again ex- 

 posed to heat in a crucible. The product is then 

 digested in muriatic acid, which dissolves the alkali, 

 and leaves the silver in its metallic state. 



A more easy way of assaying the mercurial ores is 

 to reduce them to powder, and to mix them with one- 

 fourth part of lime, and as much iron filings, and then 

 expose them to heat in an iron or earthenware retort, 

 by which the mercury is expelled, and is collected in 

 a receiver. 



Manganese. 



Manganese is not used in the arts in its metallic 

 state. The black oxide, which is a native production, 

 answers, without any preparation, all the purposes for 

 which the metal is employed. 



Zinc. 



Metallur- 

 gy- 



The ores of zinc used in metallurgy, are calamine Zinc. 

 and blende. From these the metal is procured by a 

 very simple process. The ore, after being hand-dress- 

 ed, to free it from foreign matter, is roasted, by which 

 the sulphur of the former and the acid of the latter 

 are expelled. The product is then washed, by which 

 the lighter matter is separated, and the heavy part 

 which remains is mixed with one-eighth of its weight 

 of charcoal. The mixture is next reduced to powder 

 in a mill, in which state it is put into the pots to be 

 smelted. The pots in which the smelting is perform- 

 ed resemble oil jars in shape. Through the bottom of 

 each there passes a tube, the upper end of which ter- 

 minates by an open mouth near the top of the pot, the 

 lower end goes through the floor of the furnace into 

 water. The pots are filled to the upper end of the 

 tube with the mixture of ore and charcoal, and an in- 

 tense heat is applied to them, by means of a furnace. 

 As the ore is reduced, the zinc is volatilized, and es- 

 capes through the tube into the water, where it is con- 

 densed in the form of globules. These are afterwards 

 melted and cast into moulds. 



Zinc, as thus procured, is not pure ; it almost al 

 ways contains iron, manganese, arsenic, and copper. 



To free it from these, it is again melted, and then 

 well stirred along with sulphur and fat, the former of 

 which combines with the foreign metals, and leaves the 

 zinc nearly pure, while the latter prevents this metal 

 from being oxidated. 



Assay. The assay of zinc ores may be performed Away, 

 in two different ways. 



The simplest is reducing the ore by charcoal. For 

 this purpose, after being freed from impurities, it is 

 roasted, to drive off the sulphur. It is then mixed 

 with one-half its weight of charcoal in powder, and 

 exposed to a strong heat, for about an hour, in an 

 earthen retort, the mouth of which terminates in wa- 

 ter. The zinc condensed in the water and in the 

 neck of the retort is collected and weighed. 



The second method of assay is to expose to a strong 

 heat for about an hour the mixture of ore and char- 

 coal, in a covered crucible with slips of copper, by 

 which means the two metals unite. After the pro- 

 cess is finished, the product is washed, and the weight 

 which the copper has acquired indicates the quantity 

 of zinc in the ore. 



Bismuth. 



Bismuth occurs native and mineralized by oxygen Biemuth. 

 and sulphur, and is very easily obtained from its ores. 



When native bismuth, and the oxide, are employed to 

 yield the metal, they are merely exposed to heat, in 

 contact with fuel, generally in shallow pits dug in the 

 earth. The metallic matter which collects at the bot- 

 tom is then mixed with an equal weight of black 

 flux, and put into a crucible, and covered with com- 

 mon salt, to about the depth of half an inch. A strong 

 heat is applied for a short time, by which the mixture 

 fuses, and the bismuth collects at the bottom of the 

 pot. 



Instead of the above process, the ore is sometimes 

 mixed with half its weight of borax and of pounded 

 glass, and subjected to heat in a crucible lined with 

 charcoal. 



