According, then, to the quantities of lead and silver present in the ore, the whole or part of these metals will have been dissolved by this second acid, but portions of these may, and generally do, remain mixed with the gangue as chlorides. .

If again this solution of the lead and silver chlorides.in hydrochloric acid, resulting from this second, attack, be decanted into another vessel containing: a fresh charge of calcined ore, it will take up more zinc and copper, and becoming partially neutralized, most of the lead and silver will again separate and fall down as the liquor cools, so that the clear liquid may be drawn off nearly free from these two metals.

These operations being completed, the first vessel where the ore was attacked, which for clearness may be called A, will contain a gangue together with more or less lead and silver chlorides, this gangue being still wet with some of the acid liquor of the second attack containing iron sesqui - chloride. The ore, on the other hand, in the second attacking - vessel, called B, will have lost most of its zinc and copper, but will have got added to it some of the lead and silver drawn over from A by the second acid. By boiling the partially saturated acid with the fresh ore in the second vessel B, allowing it to settle, and decanting the liquor off, it is feasible, with the application of a fresh charge of acid, to chloridize all the lead and silver in the new batch of ore in B, and by decanting B once more on to a fresh charge of ore placed in A, nearly all the lead and silver this acid had taken up'can again be precipitated on cooling, and so on ad infinitum, always obtaining as residues, on the one hand, the decanted (partially neutralized and cooled) liquors, rich in zinc or copper, but poor in lead or silver; and, on the other hand, gangues wet with acid, and containing the lead and silver completely chloridized.

Were these liquors decanted off quite neutral, they would retain and carry over in actual solution but insignificant traces of lead or silver, and nearly the whole of these metals would remain with the gangue as chlorides when settled. In practice, however, where speed is desirable, it is not convenient to obtain them so, since they have to be decanted while still hot. Some traces of these metals are therefore still - - carried - oyer in the. hot decanted liquors, but these, weakly acid zincous and cupreous liquors, when .allowed to - stand and cool,.deposit nearly every trace of the lead.and. silver, chlorides they may have carried over, whether in suspension or in actual - solution.

The acid zinc liquor derived from the attacks of the several batches of ore by the hydrochloric acid, holds, besides zinc and copper chlorides, the chlorides of any other soluble bases the ore may have contained, usually iron, alumina, lime, and often some soluble silica. If this liquor be simply neutralized with chalk, i.e., if chalk be added and stirred up with the liquor till a further addition, ceases to cause effervescence, the iron and alumina present are for the most part precipitated, only that iron remaining in solution which the calcined ore may have afforded as protoxide or sulphide. It the liquor be now decanted through a filter, this precipitated iron, together with any excess of chalk which may have been added, as well as the silica and alumina present, are retained, while the liquor passes off containing the copper and the zinc. If the work has been carefully conducted, no more than 4 gr. of silver to each cub. ft. of zinc liquor should remain in solution, and even this silver, if it be considered worth while, may be collected by some spongy lead reduced by means of spelter from a solution of lead chloride in brine.

The copper and these traces of silver may also be conveniently extracted by immersing bits of spelter or scrap zinc in the neutralized filtered solution; and finally, the zinc may be extracted as oxide by heating the solution to boiling, and' treating it, while boiling, with the least possible excess of lime in the form of milk of lime.

The actual quantity of hydrochloric acid to be employed in the attack will of course depend in each case on the composition of the ore to be treated. In treating the Welsh bluestone already mentioned, about 6 1/2 or 7 parts of acid, of 15 per cent. HC1, to 1 of calcined ore, may be used; but the quantity is easily adjustable for each kind of ore by an experiment in the laboratory on a small scale, or the quantity requisite may be calculated on an analysis of the ore. In practice it is found that even if double the amount of real - HCl bo employed which would be requisite for attacking and chloridizing the - soluble bases (not including the iron the ore may contain), the solutions run off will not retain more than mere traces of lead or silver on cooling. Thus the zinc, and for the most part the copper, as chloride, may be separated and decanted off from the lead and silver chlorides which are left insoluble in the cooled liquors or with the gangue.

If now a quantity of strong brine (say 10 gal. of brine to every 4 lb. of lead the charge of ore may hare contained) be next heated to boiling, and flushed hot on to the mixture of gangne with the lead and silver chlorides, and boiled, those lead and silver chlorides which separated from the zinc solution on cooling being returned to the gangue, the lead and silver are entirely taken into solution; and this brine being allowed to settle and run off as hot as possible into a clean vessel, and cooled, will deposit most of its lead as chloride, but none of its silver, this latter metal being retained entirely in solution, provided it be not present in larger proportion than about 1/56 part of the lead, or providing there be at least about 10 gal of brine to every 1.8 oz. of metallic silver the ore contained. Silver rarely occurs in larger quantity than this; but if it does, the quantity of brine must of course be increased and apportioned to it, so that all the silver may be taken up and retained in solution on cooling.