involved in the Construction of Artillery. 



227 



as already noticed, it is not improbable that the latter, at the high temperature 

 of fusion, may, in the processes of fusion, pouring, &c., combine with oxygen from 

 the atmosphere, and give rise to the vesicular structure by the evolution of 

 volatile matter, such as carbonic oxide, within the mass. The combination, 

 like the absorption of oxygen, taking place at a higher temperature, and the 

 subsequent evolution at a lower and definite one, at which the affinity of the cop- 

 per, or its alloy, for either the absorbed oxygen, or the absorbed carbonic 

 oxide, is a minimum. 



While, therefore, increase of volume may occur in the central mass of the 

 more fusible alloy of the gun, owing merely to some changes of molecular 

 arrangement at the instant of its consolidation, (in accordance with many ana- 

 logous cases), the whole increase, does not appear due to this, but also to the 

 sudden evolution of gaseous matter (oxygen, or its compounds, with carbon) 

 derived from the oxides or from absorbed oxygen and carbon within the mass, 

 at the moment of consolidation, and the sudden elastic evolution of part of which, 

 at the head of the casting, causes the sputtering, &c., already described. 



166. The constitution of the alloy changes, not only in the cooling, but in 

 the melting, by the continual reduction of the quantity of tin, which oxidates 

 much faster than the copper, though the latter be present in so much greater 

 mass. Dussausoy found that gun-metal having the proportions of 100 copper 

 and 1 1 tin, by weight, had the following constitutions after each of six conse- 

 cutive meltings, indicating the rapidity with which oxidation of the tin occurs: — 



The extreme irregularity of the specific gravities that he gives attached to 

 each, prove the extent to which the oxides become involved in the mass, and the 

 latter is rendered "boursouffld" thereby. It is probably in virtue of the reduc- 

 tion again of these disseminated oxides, by an elevated heat, that the opinion 



