424 Mr, A. Dick's Contributions to the Metallurgy of Copper, 



successfully applied to the casting of copper cylinders for calico 

 printing, or other objects where great soundness is required. 



The remarks which were made on page 420, in regard to the 

 possibility of sulphur, and not carbon, having affected the result, 

 apply equally to the evolution of gas described above. 



The difference in the structure of copper cast dense and porous 

 produces other effects, such as difference in colovir. This depends 

 upon the manner in which the light falls upon the fractured 

 surface. In certain positions the colour of the fractured surface 

 of an ingot of vesicular structure resembles that of one of dense 

 structure, but does not show the silky lustre. When, however, 

 the fracture of the vesicular ingot is so arranged that the light 

 falling upon it shall enter the small cavities and be reflected 

 from them to the observer, it then shows a fine salmon-red 

 colour, which the fractured surface of a dense ingot shows in no 

 light. This evidently arises from the numerous reflexions which 

 the light undergoes 'in the cavities, whereby it becomes much 

 deepened in colour. 



The metal seems to be possessed of the same malleability and 

 ductility whether dense or porous ; the brittleness of overpoled 

 copper arising, as has been stated, from impurities in the metal, 

 and not from its vesicular structure, as was proved by getting a 

 small porous ingot, made from electrotype copper melted under 

 charcoal and cast in air, rolled into sheet and drawn into wire. 

 No experiments wei'e made to ascertain whether the wire made 

 from a porous ingot was as great in tenacity as that made from 

 a dense one, nor as to what was the effect of corrosive liquids 

 upon sheet made from such ingots. A porous ingot, previous 

 to hammering or rolling, held in a vice and struck with a 

 hammer, breaks with ease when compared with a similar one 

 of dense structure. 



The specific gravity of electrotype copper, melted under char- 

 coal and treated in various ways, is shown in the following 

 Table :— 



Piece of an ingot cast under ordinary circumstances, 1 s-fj^f^ 



and therefore vesicular J 



Another piece of the same ingot 8*505 



Wire before annealing, made from the same ingot . 8'916 



Same wire after anneahng 8*919 



Piece of an ingot cast in a mould containing suffi-^ 



cient charcoal powder to cover the surface of the > 8*946 

 metal and exclude the action of the air ... J 



Another piece of the same ingot 8*952 



Piece of another ingot cast in the same manner . 8*922 

 Wire before annealing, made from the latter ingot . 8*953 



