Metal Working Metals 33 



It is difficult to solder, though some success has attended the 

 author's attempts to solder this material with a fluxless solder 

 consisting of 92 per cent, tin and 8 per cent, zinc, using an alu- 

 minium bit " tinned " with the same solder, and having all sur- 

 faces cleaned by strong potash solution, rinsed in hot water, 

 dried and heated before commencement. 



Riveting is, of course, a satisfactory method of jointing, but 

 the aluminium rivets have to be made by the worker. 



Platinum is mainly of use to the apparatus maker when it 

 is necessary to lead an electric current through glass. The fact 

 that its coefficient of expansion is almost identical with that of 

 glass renders this metal peculiarly serviceable in this respect, it 

 being the only one that can safely be used for such a purpose. 

 Were platinum cheaper, its intrinsic properties would make 

 it the most useful and widely used of metals in chemical and 

 physical laboratories, but its price is prohibitive. Would we 

 could rediscover some of the cargoes of " Little Silver " thrown 

 away by the Spaniards ! Platinum is practically non-corrosive, 

 is easily worked cold, bending with little danger of breakage, 

 and being readily hammered into any desired shape. It welds 

 easily, consequently jointing offers no trouble, and no foreign 

 metal or solder need be used. This, in itself, is a property of 

 immense value in the manufacture of physical apparatus. 



Silver is a metal much used in the making of scales and 

 mirrors. Its principal value in apparatus making arises from 

 its softness in working, which makes engraving easy; its 

 ductility, which ensures freedom from fracture ; its brightness 

 (partly due to the softness of the metal) and ease of burnish- 

 ing, and a certain resistance to corrosion. Silver is, however, 

 attacked by ammonium salts, particularly the chloride, by 

 common salt, and by nitric acid, even when dilute. Though it 

 tarnishes in a laboratory the atmosphere of which frequently 

 contains sulphur compounds, the tarnish is easily removed 

 by a chamois leather dusted with precipitated chalk or with 

 rouge ; and as apparatus having delicate silver scales is usually 

 of a type kept in cases, this disadvantage is not serious. Silver 

 is an easy metal to work, turning, drilling, and moulding by 

 the hammer being carried out with ease, while the alternative 



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