512 SUMMAEY OF CURRENT RESEARCHES. 



Metallography, etc. 



Gold-copper Alloys.* — Gold and copper form a continuous- series 

 of solid solutions. Peculiarities in the hardness curve indicated, 

 however, that the equilibrium diagram was more complex than had 

 been thought to be the case, and N. Kurnakow, S. Zemczuzny and 

 M. Zasedatelev have found that the a solid solution decomposes on 

 cooling, two compounds CuAu and CugAu being formed. These 

 compounds form solid solutions with an excess of their components, 

 The microstructure of twenty-five alloys was studied. When quenched 

 from about 800° C. the alloys consisted of a homogeneous solid solution. 

 The structure of the alloys within certain ranges of composition was 

 completely changed by annealing at suitable temperatures, owing to the 

 formation of two phases. The temperatures at which the compounds 

 are normally formed on cooling were established. The specimens were 

 etched with aqua regia or by an electrolytic method. 



Failure of a Copper Steam-pipe.j — S. A. Houghton ascribes the 

 bursting of a copper steam-pipe to the injurious effects of overheating 

 during the process of brazmg. Microscopic examination of specimens 

 cut from the tulie near the place of fracture revealed the presence of 

 cracks and an excessively coarse structure, clear indications of " burning " 

 of the copper. 



" Growth " of Internal-combustion Engine Cylinders. | — J. E. Hurst 

 considers that the small changes in volume observed at the inner surface 

 of cast-iron liners of internal-combustion engines are due to expansion 

 among the grains ; the rapid succession of changes of pressure within 

 the cyhnder results in the entrance of gases and lubricant into the 

 interstices of the grains by way of the graphite plates. The lubricant 

 may be detected by microscopic examination, and is frequently trouble- 

 some during the polishing and etching of sections. 



The formation of cracks in the piston-head of Diesel engines is 

 apparently not due to growth. The piston-head is heated to a high 

 temperature at its centre. Some of the graphite is probably dissolved 

 by the iron and re-precipitated as temper carbon on cooling. This 

 repeated action sets up alternate expansions and contractions, and the 

 absorption of the graphite may leave small cavities. The temperature 

 reached is probably near the melting-point of the phosphide eutectic. 

 The radial cracks often found are probably due to a combination of 

 causes of this kind with the rapid variations in pressure. 



* Journ. Inst. Metals, xv. (1916, 1) pp. 305-32 (18 figs.), 

 t Engineer, cxxii. (1916) pp. 88-9 (1 fig.). 

 % Engineering, cii. (1916) pp. 97-98 (2 figs.) 



