[ H9 ]

com, and tapering upwards : several of these vessels areplaced along an iron range covered with sand to the thick-ness of about two inches. Great care should be taken thatthe glass be well nealed, as equal as may be in thickness,and free from blebs, for otherwise it generally cracks inthe process. The aqua fortis must be purified as for theparting assay, though it is not needful to be so curious inadjusting its strength : it ought to be strong enough tobegin to act sensibly on silver in the cold, and not so strongas to act with violence.

A gentle fire is made under the sand bath, which isincreased or diminished, according as the dissolution ap-pears to proceed slowly or hastily. Care must be had notto apply too much heat at the beginning, the liquorbeing very liable to swell up and run over the vessel;but towards the end, when most of the silver is dissolved,and the acid nearly satiated, there is no danger of thisaccident. When the menstruum has ceased to act,which is known by its growing clear, and no more airbubbles rising in it, the solution is poured off; and if, onstirring the remaining matter, any grains are perceived init, a little more aqua fortis is added, to complete the ex-traction of the silver : some use a smooth wooden rod forthe stirring, and what dissolved silver the wood imbibes,they recover by burning it. The blackish mud, intowhich the gold is reduced by the dissolution of the silverfrom it, is washed five or six times with water, and after-wards melted.

One of the principal inconveniencies, attending thisoperation, is, that the parting glasses are extremely liableto crack, from the contact not only of a cold body, buteven of the hand. Schlutter reports, that in the Hunga-rian refineries, where great quantities of gold-holding silverare parted, the glasses are secured by a strong coating, up