ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 235 



micrographs of a brass and a bronze are given illustrating the effects of 

 the reagent. The reagent is recommended particularly for the etching 

 of brass welds. 



Heat-treatment of Grey Cast Iron." — The behaviour of cast iron 

 under the influence of heat has been studied by J. E. Hurst in con- 

 nexion with the cracking of Diesel engine piston-heads, which during 

 working attain a temperature of at least 900° C. Chemical analyses of 

 different parts of cracked piston-rods show that the combined carbon 

 is gradually all converted into the graphitic form in the portion exposed 

 to high temperature. Microscopical examination showed an increase 

 in the dentritic structure and in the number of graphite plates in the 

 portion subjected to the influence of heat ; while the extreme edge of 

 the piston is directly in contact with the flame the extent of the 

 dentrictic structure is less, the graphite is more finely divided, and 

 numerous small holes appear. Experiments with samples of a high 

 phosphorus grey cast iron showed that under certain conditions — 

 annealing at high temperatures (above 900° C.) — a portion of the free 

 carbon is reabsorbed. The structure at the extreme edge of the piston- 

 head is connected with this phenomenon. Fracture ensues from the 

 internal strain caused by the slight volume-changes which accompany 

 these changes in the condition of the carbon, as well as from the weaken- 

 ing of the iron caused by the separation of carbon. 



Uniformity of a Cast of Acid Open-hearth Steel.f — The results 

 of an investigation to determine the general quality and uniformity 

 of a cast of steel from a 40-ton acid open-hearth furnace are given by 

 T. D. Morgans and F. Rogers. The steel was made for the manufacture 

 of H.E. shell, and contained approximately 0*5 p.c. carbon. Chemical 

 analyses, tensile and hardness tests, and microscopical examinations 

 were made on the top, middle, and bottom billets of each of twenty- 

 one ingots. The manganese-content showed a slight decline from the 

 first to the last ingot poured. Beyond this and the usual slightly 

 higher percentage of elements found in the upper parts of the ingots, all 

 properties approached a high degree of uniformity. The structure 

 consisted of a ferrite network, whose meshes were filled with generally 

 lamellar jDearlite. Towards the edge of the billets the network size was 

 smaller, and was largest towards the centre. No variation in structure 

 which would prove detrimental to the steel in use was found. 



Microstructure of Commercially Pure Iron between Arg and Ar.^J 

 ■ The very pure iron (99*84 p.c. iron) known as "Armco" iron, which 

 is made in the ordinary basic open-hearth furnace, is peculiar in show- 

 ing brittleness when subjected to mechanical treatment between 900° 

 and 800° C. ; at any other temperature outside this range the material 

 is remarkably ductile and malleable. The cause of this unusual red- 

 shortness has been investigated by ^Y. J. Brooke and F. F. Hunting by 



* Journ. Iron and Steel Inst., xcvi. (1917, 2) pp. 121-8 (8 figs.). 

 t Journ. Iron and Steel lust., xcvi. (1917, 2) pp. 209-18 (21 figs.). 

 X Journ. Iron and Steel Inst., xcvi. (1917, 2) pp. 233-9 (14 figs.). 



R 2 



