Mr, A, Dick's Contributions to the Metallurgy of Copper. 423 



Instead of the ridge oa the surface, as tliere is when the air is 

 allowed free access to the metal while pouring, there is a depres- 

 sion. This depression shows very markedly the crystalline 

 structure of the metal; for during the contraction attendant 

 on solidification, the still liquid portion seems to have been 

 drawn into the central portion of the ingot, thus rendering evi- 

 dent the crystals which had formed ; this is especially evident in 

 the depression. It is not improbable that the movements of 

 different parts of the metal during solidification, by mixing por- 

 tions containing oxygen with other portions containing carbon 

 or sulphur, may be one reason why the gas evolved is especially 

 e\'ident then. This difference, produced by pouring the metal 

 into an oxidizing or reducing atmosphere, was observed very 

 many times ; and it was found quite easy, by arranging the 

 moulds beforehand, to cast one ingot which should be vesicular 

 and another which should not, from the same crucible, — casting 

 the one immediately after the other in any order. 



If it is desired to cast the metal which has been melted under 

 charcoal perfectly free from cavities, the utmost precautions must 

 be taken to exclude air. The method which was found to suc- 

 ceed best, was to place on the crucible a lid just large enough 

 to cover it, having two holes in its circumference. A cover of 

 sheet iron having two holes in it was likewise placed on the 

 mould, which was kept full of coal-gas by passing a current of it 

 in at one hole and allowing it to escape at the other. When the 

 metal in the crucible was melted, it was poured into the mould 

 through one of the holes in the lid of the crucible. The small 

 quantity of air which entered at the other to supply its place 

 would be instantly deoxidized by the carbon, whilst the metal 

 was prevented from absorbing oxygen while passing from the 

 crucible into the mould bjr the stream of escaping coal-gas 

 through which it was poured, care being taken to arrange the 

 crucible so that the metal should pass only through the gas, so 

 as to prevent any possibility of air affecting the result. Copper 

 which has been so cast resembles tough pitch copper in general 

 appearance on the fractured surface. It seems to be possible to 

 modify it slightly by the rapidity of cooling, but sufficient expe- 

 riments on this point have not been made to admit of any gene- 

 ralizations. It may likewise be cast with a dense structure by 

 placing in the ingot mould some fine charcoal powder, and hold- 

 ing the crucible as near the mould as possible, so that the metal 

 whilst being cast is exposed to the air only for an exceedingly 

 short time, because the instant it reaches the bottom of the 

 mould its surface becomes covered with the charcoal powder. 

 This method of casting copper, after fusion under charcoal in 

 coal-gas, so as to obtain a dense structure, might perhaps be 



