BRASS 



471 



Tombak, or Eed Brass, in the cast state, is an alloy of copper and zinc, containing 

 not more than 20 per cent, of the latter constituent. The following varieties are dis- 

 tinguished: 1, 2, 3, tombak for making gilt articles ; 4, French tombak for sword- 

 handles, &c. ; 5, tombak of the Okar, near Goslar, in the Hartz ; 6, yellow tombak of 

 Paris, for gilt ornaments ; 7, tombak for the same purpose from a factory in Hanover ; 

 8, chrysochalk ; 9, red tombak from Paris ; 10, red tombak of Vienna. 



Mr. Holtzapffel, in his ' Mechanical Manipulation,' has given some very important 

 descriptions of alloys. Prom his long experience in manufacture, no one was more 

 capable than Mr. Holtzapffel to speak with authority on the alloys of copper and zinc ; 

 and from his work, the following particulars have been obtained : 



The red colour of copper slides into that of yellow brass at about 4 or 5 ounces 

 of zinc to the pound of copper, and remains little altered unto about 8 or 10 ounces ; 

 after this it becomes whiter, and when 32 ounces of zinc are added to 16 of copper, 

 the mixture has the brilliant silvery colour of speculum metal, but with a bluish 

 tint. 



The alloys from about 8 to 16 ounces to the pound of copper are extensively 

 used for dipping, a process adopted for giving a fmo colour to an enormous variety 

 of furniture work. The alloys with zinc retain their malleability and ductility well 

 unto about 8 or 10 ounces to the pound ; after tins the crystalline character slowly 

 begins to prevail. The alloy of 2 zinc and 1 copper may be crumbled in a mortar 

 when cold. In the following list, the quantity of zinc employed to 1 Ib. of copper 

 is given: 



1 to 1-J oz. gilding metal for common jewellery. 



3 to 4 oz. Bath metal, pinchbeck, Mannheim gold, Similor ; and alloys bearing 



various names, and resembling inferior jewellers' gold. 

 8 oz. Emerson's patent brass. 

 10| oz. Muntz's metal, or 40 zinc and 60 copper. 'Any proportions,' says the 



patentee, 'between the extremes, 50 zinc and 50 copper and 37 zinc and 63 



copper, will roll and work well at a red heat.' 

 16 oz. soft spelter solder, suitable for ordinary brass work. 

 16.J oz. Hamilton and Parker's patent mosaic gold. 



Brass is extensively employed for the bearings of machinery. Several patents have 

 been taken out for compositions varying but slightly. The following, for improve- 

 ments in casting the bearings and brasses of machinery, appears important : Mr. 

 W. Hewiteon, of Leeds, directs, in his patent, that the proper mixture of alloy, copper, 

 tin, and zinc, should be run into metal or ' chill ' moulds, in place of the ordinary 

 moulds. In large castings, it is found more especially that the metals do not mix 

 intimately in cooling, or, rather, they arrange themselves into groups when cast in 

 gand, and the bearings are found to wear out more quickly ; but if the bearings are 

 cast so that the alloy comes in contact with metal, the mixture is more intimate, and 

 the bearings last longer than if cast in dry or green sand moulds. 



Mr. Hewitson generally only applies these chill-metal surfaces of the moulds to 

 those parts of a brass, or bearing, that are to receive the shaft or bear the axis of a 

 machine. The chills are preferred of iron, perforated with holes (^th to th inch) 



