62 ANNUAL OF SCIENTIFIC DISCOVERY. 



In European art, silver is generally the basis of what is called gold thread. 

 The silver in greatest favor Avith wire-drawers is extracted from lead. The 

 manner in Avliich the silver is separated from the lead is very simple : Avhcn 

 the lead is melted and in a perfectly liquid state, it is poured into a vessel not 

 unlike the large filters used by distillers in charging their barrels. The un- 

 der part is placed OA'er a fire, so as to keep the narrOAV or funnel portion at 

 a certain degree of temperature. The silver, being of a greater specific 

 gravity than the lead, cools more slowly. The result is, that while the 

 lead is cooling, the silver sinks or falls to the bottom, and while the lead 

 i-> becoming a solid mass, the silver retains its liquid character, and can be 

 drawn off nearly pure. Of the silver so produced, a certain quantity is 

 weighed say from 400 to 500 ounces, and placed in a crucible, Avhich is 

 placed in a charcoal fire, and there remains until the metal it contains is of 

 nearly a white heat. When heated as described, it is ready to be poured 

 into the ingot mould. These moulds arc best made of iron. The largest 

 mould is in two pieces, kept together by very strong clamps and screws, and 

 when the metal it sufficiently set, the screws are loosened, the mould sepa- 

 rates, and the ingot of silver falls easily out. The ingot so cast is about 

 two inches in diameter, and from tAventy to twenty-four inches in length. 

 The bar, or ingot, is then placed in a charcoal fire until red-hot, and after- 

 wards well hammered. This beating and hammering continues until the 

 bar is reduced to a size suitable for the first hole or die through which it has 

 to be draAvn, and is increased in length from four to five inches, or about 

 twenty per cent. The bar so prepared is pointed, and made to fit the first 

 die through which it has to pass, and laid on the draw-bench Avith the point 

 slipped through the die. The point is then seized by the jaAvs of a pair of 

 monster pincers or dnnv tongues, Avith short bow arms, at the end of each 

 of which is a hook that slips over a ring attached to the end of a strong 

 chain cable, draAvn by a steam-engine exerting the power of sixteen horses. 

 The greater the draught the tighter the grip, and the ingot passes through 

 the first die with the greatest ease, and is reduced in diameter, but increased 

 in length from ten to fifteen per cent. This process is repeated ten or twelve 

 times, each time the rod being drawn through a smaller die. As the rich- 

 ness of the wire depends upon the thickness of the gold laid on, and as all 

 the gold leaves arc very nearly, if not absolutely, of the same substance, the 

 quality of the Avire is regulated by the number of leaves placed one over the 

 other, and these vary from ten to thirty leaA'es. The bar, Avhcn overspread 

 Avith leaf, is enveloped in paper and tied tightly round Avith cord, and placed 

 in the centre of a heap of lighted charcoal, Avlicrc it remains until it assumes 

 a bright-red heat : after being burnished, and Avhen quite smooth, it is per- 

 mitted to cool gradually. 



When quite cool, the surface is covered Avith AAMX, and then commences 

 the more rapid reduction of size by draAving the bar through graduated steel 

 dies, highly polished : after Avhich it is heated and drawn through a hole, 

 which removes all Avax and dirt from the surface. 



The steel dies are then dispensed with, because, from experience, it Avas 

 found that the holes were liable to become what wire-drawers call square ; 



