A fulminating silver, differing materially from the foregoing, is frequently sold in the shops, as an object of amusement. It is enclosed between the folds of a card cut in two lengthwise, the powder being placed at one end, and the ether being notched, that it may be distinguished ; if it be taken by the notched end, and the other be held over tie flame of a candle, it detonates with a loud report and a violent flame. This compound is formed in the following manner ; but from the caution which is requisite in its manufacture, to prevent the serious effects of explosions, none but skilful and experienced chemists should attempt its manufacture. into a pint tumbler or other glass vessel are introduced 100 grains of dry nitrate of silver, over which are poured one ounce of alcohol. and the same quantity of smoking nitric acid. The mixture of the alcohol and nitric acid occasions much heat and effervescence in the liquid : if this is so violent as to overflow the vessel, cold alcohol is added, in small portions, to abate the ebullition. In a few minutes the liquor becomes turbid, and a very heavy, white crystalline powder falls down, which is separated by the filter, thoroughly washed with tepid water. Before being fully dry, it should be separated into parcels of ten or twenty grains, which portions, when thoroughly dried at a distance from the fire, present the following properties : the -substance is white and crystalline ; the light changes its colour to a dark brown. When heated, it explodes with great violence ; it explodes also by percussion and friction, and the contact of sulphuric acid ; likewise in dry chlorine gas it detonates with a loud report.
The name of separation is given to a new process for the extraction of silver from lead, invented by Mr. H. L. Pattinson, of Newcastle-upon-Tyne, and patented by him in the year 1833. It depends upon the very curious fact dis covered by Mr. Tennison, that when lead, containing a portion of silver, is melted in a suitable vessel, mid very slowly cooled, with constant stirring, at a certain temperature, small particles or crystals of solid lead begin to form in the mass c,:* liquid lead, which, being heavier than the liquid lead, sink to the ootram of the vessel, and may be removed by means of a perforated iron ladle. The particles or crystals thus separated, have the appearance of a very brilliant, coarse-grained metallic powder; and, on examination, are found to contain a much smaller proportion of silver than the original lead. Mr. Pattinson also discovered the converse of this, that, when solid lead, containing silver, is slowly and carefully heated under favourable circumstances (as in the chamber of a reverberatory furnace, supported on bars of iron at a distance from the brick-work on all sides) at a certain temperature, drops of melted lead begin to separate from it, which, on examination, are found to contain more silver than the original lead. These principles are applied in the following manner to the
extraction of silver from lead, as detailed in the specification of the patent alluded to.
" I melt a quantity of lead in an iron pot, and, after skimming off the impu rities, I allow it to cool slowly, taking care to break off and mix with the fluid mus from time to time, the parts that may congeal on the sides of the pot ; •when the temperature has become sufficiently reduced, small solid particles of lead, resembling crystals, begin to appear on the surface, and in the mass of melted metal ; which solid particles, or crystals, as they continue to form, sink down to the bottom of the pan, and, in a little time, are found in considerable quantity. I then take an iron ladle, perforated with a number of holes, with which I remove these small particles or crystals of solid lead, allowing the fluid portion to drain out from among them into the pan. I then place the crystals (either in the ladle used to remove them from the pan, or in another suitable per forated vessel) in the chamber of a reverberatory furnace, which is made for the purpose unusually large; and, in this chamber, when heated to a proper tempera ture, I drain or melt out from among the smell solid particles or crystals, a further quantity of fluid lead, leaving the residual lead in the ladle, or other vessel, almost entirely deprived of its silver; after which, this residual lead is with drawn from the furnace, melted in another pot, and cast into pieces for sale. The lead which drains out from among the crystals in the reverberatory fur nace, is, from time to time, added to the lead in the pan whence the crystals are taken ; and in this way I proceed until the original lead submitted to the operation is reduced to about one-third, which, containing nearly the whole of the silver held by the original lead, is afterwards refined in the usual way." We are informed, that in practice it is found better to confine the process to mere crystallization of the lead, without draining it in the manner described above. The poor lead obtained by the first crystallization is melted and crystal lized a second time ; and, if necessary, this poor lead is crystallized a third time, or until it is almost entirely deprived of its silver. The number of crystalli zations necessary, depends upon the amount of silver held by the original lead ; but by two or three crystallizations, lead, containing ten or twelve ounces of silver per ton, can be separated into one part rich lead, and four or five parts poor lead ; the latter holding no more than four to six pennyweights of silver per ton. This process is now in extensive operation in the various lead dis tricts of the kingdom.