Year: 1875

CT IL IS reduced tO more or less fine powder. In some establishments they content themselves with this one wash ing; but the best is 10 place two or

 three teaching boxes. one above the other, and let the liquid of the first pass 70 the second, charged with ore like the other, and so on to the third; for Tn this manner and passing three new so-

 lutions of hyposulphite, one will be more sure that the last will have dis-s solved all the silver that the ore con-

 tained; which. by the way, may be as

 certained by gathering in a glass lit

 tie of the liquid which comes through

 the faucet and testing IL with sulphide

 of calcium; it will give a characteris- tic black precipitaJe if the dissolving liquid still contains silver At the commencement of the operation the three boxes are charged and the ore of the Uppermost, after three washings, is taken away and replaced by tbat of the second one, into which that of the first is placed and so on. Two advantages are thus obtained: The economy of the hyposulphite and the certainty of extracting all the silver contained in the ore.

 From the last box the dissolving liq- uid is directed to the tubs, also of wood,

 in which the precipitation is made, for

 which purpose the apparatus is so dis

 posed that, if one tub is full, the liquid of the last teaching box can be passed to the next tub. If the first tub is fill

 ed as much as desired, the same leach

 ing is then gradually added that was

 used for the formation of the hyposul

 phIte of lime before adding to it the sulphate of copper; the silver then pre- cipitates itself into the state of sul-

 phide in the same manner as the cop per did.

 In order not to guess and to make the operations with more certainty, measure in a vessel of known capacity aquantity of the liquid which contains

 the dissolved chloride, and measure also the quantity Of solution of sulphur necessary to precipitate the silver

 which it contains, and as the capacity of the tub is known, it is easily calcu- lated how much of the precipitating agent may be needed As this opera ton is not performed with the same precision which is fixed by the alcali- matric analysis, take in a glass, after having placed all the precipitating matter, or when a little still remains to be added, some of the liquid which the tub contains, let it stand a moment, add few drops of solution of sulphur, and if it gives a precipitation or turns black, it is because there is still some unprecipitating matter 10 be added, un- ul after repeated tests no more precipi- tate is found nor any more darkening of the liquid occurs. When enough precipitating matter has been put in. which may be ascertained by adding solution of chloride of silver to the liquid taken from the tub, if no reac- ton is produced in the sulphur, which in case of containing an excess of sul- phide of calcium, will also give the precipitate of sulphur or turn black; then add little by little solution of chloride of silver of that which comes from the boxes, until it no longer pre- cipitates. That is done with the object of making again use of the original waters as dissolvers, having separated the sulphur from the silver, for if no hyposulphite of lime would remain in them and they should be used the sil- yer would be lost in the first box and become sulphide of silver.

 In order to ascertain that no excess of precipitating matter has been used, the solution of another metal whose sulphur is black, may serve; for in stance that of the copper which served for the preparation of hyposulphite, or that of acetate of lead, or another.

 When the precipitation is finished the contents of the tub are allowed to stand that the sulphide of silver may settle, which will take place in a short time. Once settled, the liquid which covers the preCipitated metal is taken out and carried to the depository, whence it is taken to the first box. The sulphur is separated, placed in a can vass bag that it may drain of, then it is pressed in a screw press made with two blanks or in anyOther best adapted manner; then it is placed in a small reverberating furnace, the reverbers tion is carried on with very moderate fire, that the sulphide of silver may not melt without being decompOsed; two hours tO two hours and half are generally needed to reduce the sulphur and bring forth the silver in the metal lie state.

 Having taken the silver from the fur mace, it is melted either in vases or re furnaces or in crucibles; in either case 1t is well to stir it with aD iron rake, which deprives it of the sul, phur that may still remain, converting itself into sulphide of iron, forming a black crust; or else so as not to uncov-