198 



been given by him with certainty, nor since verified by other 

 observers. Hence any instance ofsuch a chai'acter, or tendency 

 towards itjis worthy of attentive consideration ; anditwaswith 

 this view that the author brought before the Academy the 

 following notice of the occurrence of an alloy of copper, in 

 two states, having totally different sensible and physical 

 qualities, while identical in chemical constitution. The alloy 

 in question, in its original or normal condition, was in fact a 

 species of brass ; and the particular specimen presented to 

 the Academy was a portion of one of the brass bearings, or 

 beds, in which the principal shaft of a large steam engine re- 

 volved. 



The bearing, or bed of a shaft (as is generally known), 

 consists of a hollow cylinder, generally of brass, divided in 

 two by a plane passing through the axis ; its inner surface is 

 finely polished, and sustains the shaft, during its revolution, 

 which is also polished ; the cavity of the brass being com- 

 pletely filled by the shaft, which, in the present instance, was 

 of cast iron, and about nine inches in diameter. 



It frequently happens, notwithstanding the polish of both 

 metallic surfaces, and the application of oil, that the friction 

 due to their rapid passage over each other, while exposed to 

 undue or irregular pressure, produces a considerable rise of 

 temperature, and the brass becomes abraded. Its particles 

 have no coherence, and much resemble the " bronze powder" 

 used by painters. 



In an instance, however, which some time since came 

 under the author's notice, a different result took place. The 

 minute particles of abraded brass were by the motion of the 

 shaft, during a few hours, impacted into a cavity, at the junc- 

 tion of the two semicylinders of the bearing, where they be- 

 came again a coherent mass, and when removed presented all 

 the external appearance of an ingot or piece of brass, which 

 had been poured in a state of fusion into the cavity. On 

 more minute examination, however, the mass was found to 



