82 Dr. Russell and Dr. A. Matthicsscn on the Cause 



and dried, through fused copper for five minutes. In all our ex- 

 periments electrotype copper was used, as being the purest, and 

 each experiment was made with about 150 grammes of the metal. 

 The gases experimented with were hydrogen, oxygen, nitrogen, 

 air, carbonic acid, and carbonic oxide. With each gas the expe- 

 riment was made under three different circumstances: — 1st, the 

 gas was passed through when the melted copper was without 

 flux or covering ; 2nd, when it was under a flux of salt ; and 

 3rd, when covered with charcoal. We need not describe sepa- 

 rately each experiment ; it will be sufficient to state the general 

 result obtained from this series of experiments, which is, that 

 the vesicular structure in the copper is only developed when 

 either oxygen or air is passed through the melted metal under 

 charcoal. Under these circumstances, not only did the metal 

 become very porous, but when solid the surface was found to 

 have risen or vegetated, often to a very considerable extent. In 

 some cases even small particles of the melted copper, on the 

 cooling of the mass, were projected out of the crucible. A similar 

 phenomenon is known to copper-smelters, and called by them 

 copper rain. In order to obtain satisfactory results, a consider- 

 able amount of care is necessary in performing these experi- 

 ments ; for if the surface of the melted copper towards the end 

 of the experiment be exposed, by the burning off of the charcoal 

 or any other accidental circumstance, only for a very short time 

 to the air, that alone is sufficient to induce the vesicular struc- 

 ture in the metal. Again, we found that the same phenomenon 

 was produced when any of the fuel fell into the melted copper. 

 Having satisfactorily proved that air and oxygen were the only 

 gases which caused the copper to become vesicular, and in fact 

 these only when carbon was present, we naturally concluded that 

 the vesicular structure could not be owing to any mere absorp- 

 tion or chemical combination of the melted copper and gas, but 

 was probably due to the formation of carbonic oxide arising from 

 the reduction of the suboxide of copper by means of the charcoal. 

 The following experiments show, we think, that this supposition 

 is correct : — 



Copper was fused alone in air : immediately on removing it 

 from the furnace, powdered charcoal was thrown on the surface ; 

 considerable vegetation ensued, and on being fractured it was 

 found to be very vesicular. 



Another specimen of copper was fused, as before, in the air ; 

 but now, on removing it from the furnace, instead of throwing 

 charcoal on the surface of the melted metal, a jet of coal-gas was 

 allowed to play upon it. The result was precisely similar to 

 that obtained with the charcoal, the carbon from the coal-gas 

 reducing the suboxide. 



