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Pure Sea-Salt

Boil together for a few minutes, in a glass vessel, a solution of salt with a little pure bicarbonate of soda; filter; add muriatic acid until the liquor be neutral to litmus and turmeric paper; then evaporate and crystallize. 3210. Το Extract Silver from Lead.

This is easily done in a small way by melting the mixed metals by a strong heat in the open air. The lead will be converted into litharge, and the silver will sink to the bottom of the crucible. On a large scale, the silver is extracted from the lead by the oxidation of the lead into a reverberatory furnace of a particular construction. A shallow vessel, called a cupel, is filled with ashes, well packed and pounded down, and a cavity cut out for the reception of the nozzle of a bellows, through which air is forcibly driven. When the fire is lighted and the lead is in a state of fusion from the reverberation of the flame, the blast from the bellows is made to play forcibly on the surface, and in a short time a crust of oxide of lead or litharge is formed and driven off to the side of the cupel opposite to the mouth of the bellows, where a shallow aperture is made for it to pass over; another crust cannot be too much insisted on. (Cooley). of litharge is formed and driven off, and this

3207. Assay of Silver by Chemical Analysis. Dissolve 10 grains of the alloy in 100 grains of nitric acid, specific gravity 1.28, by the aid of heat; the solution being is repeated until nearly all the lead has been scorified and blown aside. The completo separation of the lead is indicated by the appearance of a brilliant lustre on the convex made in a tall stoppered glass tube, furnished surface of the melted mass in the cupel, which with a foot; then place it in a very delicate is occasioned by the removal of the last crust balance, which must be brought into an exact of litharge which covered the silver. If the state of equilibrium, and add the test solution silver thus abstracted is not sufficiently pure, (see No. 3208) gradually and cautiously, until it is further refined in a reverberatory furnace, the whole of the silver be thrown down; but being placed in a cupel lined with bone ashes the utmost care must be taken not to exceed and exposed to an intense heat, so that the this point. The number of grains now re- lead which escaped oxidation by the first quired to restore the equilibrium of the scales process is converted into litharge, and is gives the exact quantity of pure silver present absorbed by the ashes of the cupel. in 1000 parts of the sample. The addition of 3211. Test for Metallic Silver. the test liquor to the solution requires the compounds of silver, mixed with carbonate of utmost exactness. After each addition the soda, and exposed on charcoal to the inner stopper should be placed in the tube, and the flame of a blow-pipe, afford white, brilliant, The and ductile metallic globules, without any in a pan over the fire, when it will be ready incrustation of the charcoal. (See also As- for melting, with the usual fluxes, or re-solusaying.) tion with nitric acid. This process is rapid and easy; is not subject to loss; it will yield, in the terms of trade, pure silver, of a quality from 994 to 998 thousandths fine, and is therefore well adapted to the preparation of pure nitrate of silver for the use of photographers and all others who need a reliable article.