of Vesicular Structure in Copper. 83 



In another experiment of the same kind we varied the condi- 

 tions by throwing on the charcoal before the fused copper had 

 been removed from the furnace ; a vegetation in bulk nearly 

 equal to half that of the copper used took place. In order to 

 give a more definite idea of the great extent to which the metal 

 becomes porous, we have taken the specific gravity of several of 

 these specimens of copper in which we have developed the vesi- 

 cular structure. The specific gravity of the copper operated on 

 in the last experiment was foujid to be only 5*683, whereas that 

 of pure copper is 8*952. Mr. Dick, in the paper before alluded 

 to, describes some very interesting experiments which he made 

 by casting copper which had been fused under charcoal in an 

 atmosphere of coal-gas, thus not allowing the melted metal to 

 come in contact with the air ; the result was that he then ob- 

 tained a perfectly solid casting ; but if, instead of using coal-gas, 

 he made the casting in air, using even metal out of the same cru- 

 cible in both experiments, he in the latter case always obtained a 

 casting which was very vesicular. Our experiments entirely 

 confirm these results of Mr. Dick. The specific gravity of the 

 casting thus obtained shows in a striking manner the great altera- 

 tion in the density of the copper. A specimen of the electrotype 

 copper which we used, simply fused and allowed to cool under 

 charcoal, gave us a specific gravity of 8*952. The casting made 

 in coal-gas had a specific gravity of 8*929 ; another made in the 

 same way had a specific gravity of 8*919; whereas a third spe- 

 cimen, also made with metal out of the same crucible, but cast in 

 air, had a specific gravity of 6*193. To render our experiments 

 still more conclusive, we now fused copper, allowing the air free 

 access to it, and cast one portion of the metal in moulds contain- 

 ing air, and the other in moulds filled with coal-gas. Two spe- 

 cimens of the copper cast in air had respectively the specific 

 gravities 8*618 and 8*665, while the specimens which had been 

 cast in coal-gas had a specific gravity of only 6*926 and 6*438. 



The cause, then, of the vesicular structure in copper appears 

 to be due to the reduction of the suboxide of copper by the car- 

 bon mechanically drawn down into the mass of the metal by the 

 currents continually formed from the cooling of the surface. 

 The carbonic oxide thus produced throughout the whole mass of 

 the copper is given off as long as the surface remains fused ; but 

 as soon as it solidifies, the crust is lifted up, and breaking, pro- 

 duces vegetation. The carbonic oxide formed at the time of soli- 

 dification not being able to escape, remains dispersed through 

 the metal, giving it the vesicular structure. With lampblack 

 (carbon in a finer state of division) instead of powdered charcoal, 

 the action appears to be still more intense ; and on throwing 

 some of it on melted copper, the evolution of gas may be easily 



G2 



