518 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and which is known to be advantageous for smooth running, results 

 from a numljer of causes, chiefly to breakdown of the surface grains 

 under the influence of alternating stresses, producing a fine structure, 

 harder and less easily disintegrated than the original coarser grained 

 structure. The peculiar anti-frictional properties of cast-iron liner 

 surfaces are probably due to their similarity in structure to that of 

 anti-friction alloys ; the hard constituents standing in relief provide 

 support for the load, while the minute hollows resulting from disinte- 

 gration of the soft constituents provide distributing reservoirs for the 

 oil, ensuring effective lubrication of the whole surface. Micro-structural 

 arrangement will thus have an important influence upon the anti- 

 frictional properties of cast-iron. Owing to the heterogeneous character 

 of cast-iron, the Brinell hardness numeral affords no true indication of 

 its resistance to wear. The method of internal grinding for finishing 

 liner surfaces is superior to machining, as being less liable to leave small 

 pits and surface cracks, which are almost always found however slow 

 the rate of machining. Ground surfaces also possess in a degree the 

 glazy appearance of a finely granular flowed structure. 



Machining Properties and Structure of Brass."' — Stampings (hot 

 forged) of 00 : iO brass having Brinell hardness numbers much above 

 70 proved difficult to machine, while cold-rolled rods of similar com- 

 position were machined readily when the hardness number was as high 

 as 140. An explanation is suggested by 0. W. Ellis based upon the 

 differences in structure of the stamping and rod. The arrangement of 

 the (i constituent — in irregular distributed crystaUites of no definite 

 orientation in the stamping and in elongated almost continuous crystal- 

 lites parallel to the axis in the rod — produces a similar structure on a 

 transverse surface in both cases, i.e. in cutting through the rod at right 

 angles to the axis, a similar amount of hard material requires to be 

 removed to that required to be removed in cutting a section of the 

 stamping of similar thickness, but the more stable arrangement of the 

 yS constituent in the rod offers greater resistance to deformation during 

 Brinell testing. 



Structure and Electrical Conductivity of Copper.t— In a general 

 account of the production and properties of electrolytically refined 

 copper, F. Johnson refers to the relation between structure and electrical 

 conductivity. All impurities per se have a lowering effect on the 

 conductivity of copper, but those elements which enter into solid 

 solution exert a much greater effect than those such as oxygen which 

 form intercrystalline matrices. Soluble impurities appear further to 

 produce a greater depression of conductivity when they enter into solid 

 solution as a compound, e.g. arsenic, antimony and phosphorus. The 

 effect of soluble impurities is not much different whether they are 

 concentrated at the crystal boundaries as in the cored structure of cast 

 arsenical copper, or whether as in annealed copper diffusion has equalized 

 the concentration throughout. Photomicrographs of copper containing 

 0-20 p.c. of oxygen as cast and after annealing for five hours at 900° C. 



* Journ. Inst. Metals, xvii. (1917, 1) pp. 44-5. 



t Journ. Soc. Chem. Industry, xxxvi. (1917) No. 14, pp. 803-8 (2 figs.). 



