1900.] on TJie Structure of Metals. 421 



It was shown that certain crystals, more aggressive than their neigh- 

 bours, grew by absorbing other crystals, the process of growth usually 

 taking place by a crystal's throwing out skeleton arms to form a net- 

 work, the detail of which became tilled up later as the process of 

 growth continued. 



Professor Ewing concluded by stating a theory which Mr. Rosen- 

 hain had advanced to explain the process of crystalline growth in a 

 solid metal. According to this, the action occurs through solution of 

 the metal into and deposit from the film of eutectic alloy, which forms 

 a cement between one crystal and another. This eutectic is due to 

 the presence of impurities. It appears probable that the action is 

 electrolytic, for it is only after straining has broken the films of 

 eutectic, and has brought the crystals into contact, that the process of 

 growth occurs. This theory received much support from what was 

 observed to happen in the case of welds. Two freshly scraped sur- 

 faces of lead could readily be welded cold, by application of severe 

 pressure. When subsequently heated the weld showed no crystal 

 growth across it. But when a few fragments of some metallic im- 

 purity, capable of forming a eutectic with the lead, were introduced 

 before the weld was made, subsequent heating was found to make 

 crystals grow readily across the plane of the weld. This confirmed 

 tho view that a film of eutectic alloy was an essential intermediary 

 in the process by which one crystal grew at the expense of another. 



[J. A. E.] 



