294 



ELECTEICITY. 



not adhere to iron. The mercury, by its affinity 

 for the silver and non-affinity for the iron, 

 stands up in alto-relief, and adheres so firmly 

 that melted wax can be poured over it without 

 disturbing it. When the wax is cold, it forms 

 a matrix for the die or type. It is coated with 

 plumbago to make it conduct electricity, and is 

 then immersed in a bath of sulphate of copper, 

 and by the ordinary electrotyping process the 

 die is deposited. 



TJie Mechanic^ Magazine of June 28th, while 

 speaking of Dulos's process as an ingenious 

 one, described a simpler method of obtaining 

 the same result. A plate of copper is made 

 perfectly level and smooth, and then coated with 

 varnish, through which the design is made, with 

 a fine steel point, cutting the bottoms of the 

 lines clean down to the copper. The whole 

 plate is then coated with plumbago, but after- 

 ward the particles of plumbago powder which 

 have fallen into the sunken lines of the de- 

 sign, must be carefully removed with a soft 

 brush. The plate is then connected with the 

 battery in the sulphate of copper bath, and the 

 die is deposited. Even this multiplied process, 

 like that previously described, is regarded by 

 the Mechanics' Magazine as no cheaper than 

 wood-engravings. These discoveries have been 

 entirely superseded by the various processes 

 for photographing and engraving on stone and 

 zinc, which have been brought to a high pitch of 

 perfection during the past year, and are now 

 largely used in this country for the reproduc- 

 tion of fine engravings and book-work. 



Separating Silver from Lead by Electricity. 

 The lead carrying the silver is melted in a re- 

 verberatory furnafce, and exposed to the usual 

 preliminary refining process by which portions 

 of copper, antimony, and other metals are re- 

 moved by oxidation. The temperature of the 

 lead is then brought to about 430 Reaumur, in 

 order that the zinc to be subsequently added to 

 it may melt in it. A quantity of zinc, about -J- 

 to -J per cent, of the charge of lead in the pot, is 

 then introduced into the lead by means of any 

 suitable instrument, and the whole thoroughly 

 stirred and mixed. An electric current, which 

 may be generated by a suitable battery, in con- 

 nection with one of Ruhmkorff's coils, or other- 

 wise, is then, by means of conductors, caused to 

 pass through the molten metal ; this current, 

 which produces among 'other effects in most cases 

 a certain tremor in the mass of metal, is contin- 

 ued for a period varying from 10 to 30 minutes, 

 according to the quantity and purity of the 

 lead under treatment, and to the proportion of 

 silver it contains. The conductors used are 

 rods of copper, with wooden handles; two, 

 four, six or eight of these may be suspended in 

 the metal in any convenient manner ; the cur- 

 rent should be continued until all the zinc has 

 reached the surface, bringing the silver with it, 

 when it ceases to have any action on the desil- 

 verizing of the lead. After the' conductors of 

 the electric current have been withdrawn from 

 the molten metal, it is allowed to remain at rest 



for about a quarter of an hour, and the crust 

 which has formed is then removed. By re- 

 ducing the temperature in this way, the alloy 

 of zinc becomes white, and separates itself 

 more readily. The temperature of the metal is 

 now raised to about 430 Reaumur, and the 

 operation of introducing from about i to -J- per 

 cent, of zinc, followed by the application of the 

 electric current and the removal of the crust, 

 is repeated in the manner already indicated. 

 When the lead under treatment is very impure, 

 or contains a large proportion of silver, it may 

 be necessary to repeat this process two or three 

 times. The silver which is contained in the 

 various crusts or skimmings taken from the 

 molten metal after each addition of zinc, and 

 passage of the electric current, may be recov- 

 ered by any of the ordinary methods. The lead 

 when sufficiently desilverized is again refined 

 in a reverberatory furnace, in order to remove 

 traces of zinc and other impurities, and may 

 then be run into ingots, for sale. (Mechanics' 

 Magazine.) 



Other Useful Applications of Electricity. 

 It is necessary that a person attending on a 

 power-loom should carefully watch and remedy 

 the breaking of a thread ; and, as several looms 

 may be in charge of one attendant, it would be 

 very useful that his attention should be direct- 

 ed at the earliest possible moment to a broken 

 thread. This is now done in the case of a 

 stocking-machine by means of electricity, and 

 the same contrivance is applicable in other 

 cases. A small lever rests on the thread, and 

 retains its position as long as the thread is 

 whole. But the instant the thread breaks, the 

 lever falls and completes connection between 

 the poles of a galvanic battery, which excites a 

 small electro-magnet, and sets a bell-ringing 

 apparatus in motion. This attracts the notice 

 of the attendant, so that the broken thread can 

 be promptly rejoined. 



An application of electricity, more curious 

 perhaps than useful, has recently been made in 

 France. Instead of placing a fulminate with- 

 in a cartridge, and thus rendering it liable to 

 explode accidentally, a very fine platinum wire 

 is inserted in it. This, by a simple mechanism, 

 is connected at pleasure with two very minute 

 galvanic batteries, which are enclosed in the* 

 stock of the musket, and becoming incandes- 

 cent, explode the powder. The arrangement 

 is not likely to be employed in practice, except 

 perhaps for artillery. 



It has been found by recent experiments 

 that electro-magnetism can be used with excel- 

 lent effect in the manufacture of iron ; the pro- 

 cess being facilitated and rendered more per- 

 fect, while at the same time fuel is economized. 

 An opening is made in the sruelting-furnace, 

 and opposite to this opening is placed an elec- 

 tro-magnet, which is excited by a current that is 

 made to traverse the iron while in a state of fu- 

 sion. Numerous gas-bubbles are produced, and 

 the resulting iron is harder and more tenacious 

 than that manufactured in the ordinary way. 



