ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 517 



at 550° C. This is the temperature at which the increase in ductility 

 due to re-crystallization and growth of a is neutralized by the decrease 

 due to separation of fi. The structures of the arsenical alloys (Jj) and (c) 

 quenched from both G50° and 750° show a pecuhar arrangement of the 

 y8 in parallel bands, which is not shown by alloy {a) similarly treated. 

 These bands occur in regions previously occupied by a of high zinc 

 content (resulting from the transformation of hot-rolled /? bands), and 

 their non-appearance in alloy {a) provides evidence that arsenic hinders 

 diffusion in these alloys. The appearance of the banded structure 

 coincides with a sharp drop in the reduction of area, but the elongation 

 is not affected to the same extent. The quenched yS phase under high 

 magnification showed a finely lamellar internal structure, which is 

 ascribed to incipient separation of a. 



In the second series of heat-treatments cold-rolled strips of each 

 alloy were annealed for fifteen minutes at 700° C. and then cooled at 

 rates of 5°, 20°, 50° and 100° per minute down to temperatures ranging 

 from 650° to 450° C. and then quenched. 450° C. was taken as the 

 lower limit of cooling, as the absorption of metastable /8 below 450° C. 

 is too slow for any change in properties to take place with the rates of 

 cooling employed. The mechanical properties produced by each heat- 

 treatment in the second series of experiments and photomicrographs of 

 typical structures are given. With alloys {a) and (c) the ductility 

 increases rapidly with the slower rates of cooling down to 600° C. ; 

 cooling to lower temperatures increases the ductility only slightly. 

 Structural observations confirm these results in showing little absorption 

 of (i below 600°. With the faster rates of cooling, however, the absorp- 

 tion of /? and consequent increase of ductility continues to 450°, but the 

 total amount of ^ absorbed is less than that which occurs in the 

 corresponding treatment with the slower rates of cooling. Alloy {h), 

 which contains nearly twice as much ji as the other two alloys when in 

 equihbrium at 700°, showed a gradual increase in ductility down to 450°, 

 whatever rate of cooling was employed. A structure in which y8 forms 

 a network round the a grains was noted to form by annealing at 

 temperatures above 600° and cooling at rates above 20° per minute ; the 

 network was absorbed on cooling at 5° per minute. 



The alloys were etched with concentrated ammonia to which a 

 little hydrogen peroxide had been added, and were subsequently given a 

 light wash of ferric-chloride solution to darken the /? constituent. 



Cast-iron : with Special Reference to Engine Cylinders."- — The 

 features of grey cast-iron which render it such a valuable material for 

 rubbing parts as in cylinders and pistons of internal combustion engines 

 have been studied l)y J. E. Hurst. Worn gas-engine liner surfaces are 

 covered with small pits. Microscopic examination shows the harder 

 constituents such as phosphide and cementite standing in relief. This 

 is considered to be clue to a polishing effect brought about Ijy surface 

 disintegrated material suspended in the film of oil. These projections 

 and other grains composing the surface of the cylinder are eventually 

 loosened and detached, leaving pits. The glazy appearance often 

 conferred on the surface of cylinders which have been in use some time, 



* Engineering, ciii. (1917) pp. 40 1, 51-4, 75-6 (21 figs.), 



