84 On the Cause of Vesicular Structure in Copper. 



seen. That the vesicular structure is not owing to any especial 

 affinity of melted copper for carbonic oxide, is shown by the fact 

 that when copper is fused under charcoal or a flux of salt, and 

 carbonic oxide passed through it, the metal, on cooling, is found 

 to be entirely devoid of all porous structure, as proved by its 

 specific gravity, which we found to be 8*943. 



That carbon can exercise an influence of the kind attributed 

 to it in the foregoing experiments, is shown by its action on 

 melted silver; for if silver be fu^ed under a layer of charcoal, 

 and oxygen gas passed through it for any length of time, still 

 no spitting will take place on the cooling of the metal. Again, 

 when silver is fused in air, if charcoal be thrown on the melted 

 surface no spitting occurs, a fact well known to assayers : sand 

 or any other body of that kind does not exercise a similar influ- 

 ence on the silver*. 



We next tried the action of sulphur on suboxidized copper, 

 and found that it also produced the vesicular structure, and even 

 caused the copper to vegetate to a very considerable extent. In 

 fact, when sulphur is thrown on copper which has been melted 

 with access of air, results are obtained similar to those which 

 carbon produces under the same circumstances. 



Two specimens of copper which had been rendered vesicular 

 by the action of sulphur, were found to have respectively the spe- 

 cific gravities of 6*6 and 5*1. It is a somewhat curious fact, 

 that the phenomenon of copper rain is caused to a much greater 

 extent by the action of sulphur than it is by carbon. The sul- 

 phur, of course, acts on the suboxide'of copper in the same kind 

 of way as the carbon ; and the vesicular structure and copper 

 rain are in this case owing to the evolution of sulphurous acid. 



We also tried the action of iodine and of phosphorus on 

 suboxidized copper, but they did not produce any appearance of 

 vesicular structure. 



The foregoing experiments were carried out partly in Professor 

 Percy's, and partly in Professor Williamson's laboratory. 



* While engaged on this subject, we also made a series of experiments 

 upon silver, to ascertain whether any other gas than oxygen was absorbed 

 by it. The melted silver was treated in precisely the same way as the cop- 

 per, and the gases oxygen, hydrogen, air, nitrogen, carbonic acid, and car- 

 bonic oxide passed through it. The spitting of the silver we found to be 

 caused only by oxygen or air, and, further, that, as mentioned above, this 

 was entirely prevented by the presence of charcoal. In Gmelin's * Che- 

 mistry ' (vol. vi. p. 139) it is stated that, when silver is fused under nitrate 

 of potash, the spitting takes place : this statement we believe to be incor- 

 rect ; for we always found that when silver was carefully fused, so that the 

 air did not come in contact with it, under a layer of either nitrate or chlorate 

 of potash, no spitting took place. As both these salts are decomposed 

 below the melting-point of silver, this result is what might be expected. 



