involved in the Construction of Artillery. 225 



164. The phenomena that attend its separation are remarkable. Some time 

 after the exterior of the gun has become solid, the still liquid interior of the column 

 of metal begins to present, at its upper extremity, intestine motions, often attended 

 ■with sputterings and jets of metal, and ending, by the upper extremity rising more 

 or less above its former limit, in an irregular fungoid form, and then becoming 

 solid. This has usually been ascribed to a change of voliune occurring in the 

 mass of the internal alloy at the moment of its consolidation, due to crystalline 

 or other molecular forces, while the sputtering and jets of metal, and the cauli- 

 flower-like top assumed by the upper end of the column of metal (the top of the 

 " rising head," or " dead head" of the gun-founder) has been ascribed to the 

 escape of air from the mould, through the still liquid metal of the interior, — an 

 attempt at explanation certainly erroneous (though copied almost word for 

 word from author to author), since any air requiring escape, from the sides of 

 the loam mould, would commence to escape through the column of metal, if 

 escaping at all through it, the moment the mould was full, when the metal is all 

 hottest and most fluid, and could not possibly escape through the central fluid 

 portion of the mass subsequently, to the consolidation of the exterior, and, 

 indeed, in no case of moderately good moulding need, or can escape, either way, 

 other channels being provided for it. The true cause of the phenomena seems 

 to be this. 



165. Copper, like silver, possesses, in all probability, the property of absorb- 

 ing oxygen when in fusion, and its alloy with tin does not appear to prevent this, 

 contrary to the case of silver, wherein a slight alloy of copper is sufiicient to 

 prevent its absorption of oxygen, which Lucas discovered was absorbed by pure 

 silver in fusion to the extent of twenty times its own volume ; the metal evolving 

 the whole of it again at the moment of consolidation by cooling, and with the 

 protrusion of similar fungoid masses, which present themselves like little craters 

 on the surface of a large ingot of refined silver. 



Direct experiment has not yet, the author believes, shown a like absorption 

 of oxygen by copper or its alloys with tin ; but that the fact is so, is indicated by 

 several circumstances. Copper possesses the utmost susceptibility to absorb 

 many other bodies while in fusion ; thus the well-known process called " poling," 

 of refining " tile copper," which is short, brittle, and incapable of being beaten 

 out, laminated, or wire-drawn, to bring it to "tough pitch," when it admits 



