584 



PLATINUM 



being held in the jaws of a vice, while the shear-shaped hammer rests upon it. By 

 striking on the head, A, while the metal plate is shifted successively forwards, the 

 beading is formed. In fig. 1629, the tooth, a, is a guide to regulate the distance be- 



1629 



1633 



tween the bead and the edge. A similar effect is produced of late years in a neater 

 and more expeditious manner by the rollers, figs. 1631, 1633. Fig. 1632 is a section 

 to show the form of the bead. The two wheels a, a, fig. 1631, are placed upon axes, 

 two of which are furnished with toothed pinions in their middle ; the lower one being 

 turned by the handle, gives motion to the upper. The groove in the upper wheel 

 corresponds with the bead in the lower, so that the slip of metal passed through be- 

 tween them assumes the same figure. 



The greatest improvement made in this branch of manufacture is the introduction 

 of silver edges, beads, and mouldings, instead of the plated ones, which from their 

 prominence had their silver surface speedily worn off, and thus assumed a brassy look. 

 The silver destined to form the ornamental edging is laminated exceedingly thin ; a 

 square inch sometimes weighing no more than 10 or 12 grains. This is too fragile 

 to bear the action of the opposite steel dies of the swage above described. It is 

 necessary, therefore, that the sunk part of the die should be steel, and the opposite 

 side lead, as was observed in the stamping ; and this is the method now generally 

 employed to form these silver ornaments. The inside shell of this silver moulding 

 is filled with soft solder, and then bent into the requisite form. 



The base of candlesticks is generally made in a die by the stamp, as well as the 

 neck, the dish part of the nozzle or socket, and the tubular stem or pillar. The dif- 

 ferent parts are united, some with soft and others with hard solder. The branches 

 of candlesticks are formed in two semi-cylindrical halves, like the feet of tea-urns. 

 When an article is to be engraved on, an extra plate of silver is applied at the proper 

 part, while the plate is still flat, and fixed by burnishing with great pressure over a 

 hot anvil. This is a species of welding. 



The last finish of plated goods is given by burnishing tools of bloodstone, fixed in 

 sheet-iron cases, or hardened steel, finely polished. 



The ingots for lamination might probably be plated with advantage by the delicate 

 pressure process employed for silvering copper-wire. 



For the processes of Electro-plating, see ELECTBO-METALLUBGY. 



PKATXXrtriMC (Sym. Pt., At. wt. 98'5). A metal of a greyish-white colour, harder 

 than silver, and of about double its density, being of specific gravity 21. It is so in- 

 fusible, that no considerable portion of it can be melted by the strongest heats of our 

 furnaces. It is unchangeable in the air and water ; nor does a white heat impair its 

 polish. The only acid which dissolves it is the nitro-muriatic. 



Native Platinum in the natural state is never pure, being alloyed with several other 

 metals. It occurs only under the form of grains, which are usually flattened, and 

 resemble in shape the gold pepitas. Their size is in general less than linseed, although 

 in some cases they equal hemp-seed, and, occasionally, peas. One piece brought from 

 Choco, in Peru, and presented to the Cabinet of Berlin by M. Humboldt, weighs 

 882J grains, or more than 2 oz. avoirdupois. A lump of native platinum is in the 

 Royal Museum of Madrid, which was found in 1814 in the gold mine of Condoto, 

 province of Novita, at Choco. Its size is greater than a turkey's egg (about 2 inches 

 one diameter, and 4 inches the other), and its weight 11,641 grains. In 1827 a speci- 

 men was found in the Ural Mountains which weighed 11 '57 pounds troy; the largest 

 yet obtained being in the Demidoff Cabinet, and weighing 21 pounds. 



The colour of the grains of native platinum is generally a greyish white, like tar- 

 nished steel. The cavities of the rough grains are often filled with earthy and ferru- 



