422 Mr. A. Dick's Contributiom to the Metallurgy of Copper. 



Other iugots have numerous large cavities among the small ones, 

 and a very rough surface produced by the small craters from 

 which the gas escaped. The specific gravity of a piece of a small 

 ingot made like the previous one, which had this appearance, 

 was found to be 8"211 ; of another piece of the same, 8'285. Of 

 course the specific gravity will vary according to the degree in 

 w^hich these cavities can be filled with water when taking the 

 specific gravity. The method pursued was to place the piece of 

 metal in boiling water and allow it to cool under water. This 

 was found to give higher results than when the same piece of 

 metal was placed in water under an exhausted bell-jar; but the 

 filling of the cavities can never be perfect, because they do not 

 communicate. The reason assigned for the well-known fact of 

 the evolution of a gas has been, that oxygen was dissolved by 

 the melted metal and expelled from it during solidification (see 

 English edition of ' Gmelin's Chemistry,' vol. v. p. 402). It 

 seems, however, certain that it cannot be oxygen, because " dry 

 copper " and " tough pitch copper," which certainly contain 

 oxygen, give off none during solidification : further, the surfaces 

 of the cavities when the ingot is fractured are seen to be perfectly 

 bright and metallic, which they would not have been had oxygen 

 been in contact with them at the temperature at which they were 

 formed. The gas seems to be either carbonic acid or carbonic 

 oxide, or it may be sulphurous acid, as is shown by the follow- 

 ing experiments. 



If a piece of copper is melted under charcoal and allowed to 

 cool in the crucible, it will be found that the appearance of the 

 fracture, though affected by the rate of cooling and other things, 

 never presents any trace of vesicular sti'ucture ; but that if, instead 

 of allowing it to cool in the crucible, it be cast under ordinary 

 circumstances into an ingot mould, then the fracture does show 

 a vesicular structure. In this case, however, another element 

 affects the result, viz. the air through which the metal passed in 

 being poured from the crucible into the mould, and also that in 

 contact with its surface when in the mould. Owing to this, a 

 portion of the copper combines M'ith oxygen ; and as this gets 

 mixed with another portion of the copper still containing carbon 

 or sulphur, it gives rise to the gas which causes the vesicularity. 

 The most curious point is, that the gas is given off just at the 

 moment of solidification, or appears to be given off only at that 

 time. But that the evolution of the gas is due to this reaction 

 is proved by the following fact. If copper is melted under 

 charcoal and poured through an atmosphere of coal-gas and into 

 an ingot mould filled with the same gas, instead of the ordinary 

 atmosphere, the metal solidifies with a bright and smooth sur- 

 face, and when fractured shows no trace of vesicular structure. 



