426 SUMMARY OF CURRENT RESEARCHES RELATING T<> 



Influence of Manganese in Cast-iron.* — F. Wiist and H. Meissner 

 have investigated the mechanical properties and the micrustrncture of 

 forty samples of grey cast-iron, falling into four series containing respec- 

 tively 2*8, 3*1, 3 " 3, and 3 ■ 9 p.c. carbon, the manganese in each series 

 ranging from about 0*2 to 1*5-2 "5 p.c. The silicon content was 

 about 1 *6 p.c. Examination of large unetched sections at low magnifi- 

 cations indicated that the proportion of primarily-separated mixed 

 crystals increased with increase of manganese. Thus the solid solubility 

 of carbon in iron containing silicon at the temperature of solidification 

 is raised by manganese, and the amount of the ledeburite eutectic is 

 diminished ; the size of the graphite flakes is also reduced. Graphite 

 was found in two forms, lamellae and small rounded inclusions which 

 had apparently been formed in the temperature interval between final 

 solidification and Ar r The pearlite was finer in structure as the 

 manganese increased. The amount of graphite formed increased with 

 increase of manganese up to * 3 p.c, but further increase of manganese 

 ii}) to 2 * 5 p.c. had no further influence on the graphite content. The 

 amount of ferrite diminished with increase of manganese. 



Meteoric Iron.f — An account of the examination of a meteorite 

 which fell at Winburg in 1881, by W. A. D. Kudge, includes a description 

 of the microstructure. The specimen consisted essentially of iron 

 containing about 7 p.c. nickel. It was formed of a mass of large ferrite 

 crystals with veins of nickel-iron alloy running through, and with flakes 

 and crystals of nickel-iron alloy disseminated throughout the mass. 

 The details of the microstructure were most clearly developed by heat- 

 tinting. The structure was considerably altered by annealing at 800° C. 



Solidification of Metals.} — C. H. Desch summarizes present know- 

 ledge on the subject of the earlier steps in the crystallization of metals 

 from the liquid state. The summary is divided into the following sections ; 

 (1) the cellular structure of metals ; (2) crystallization from centres 

 and the formation of crystallites or crystal skeletons ; (3) foam structures, 

 and Quincke's hypothesis ; (4) cellular structures in cooling liquids ; 

 (5) liquid crystals ; ((!) the influence of surface tension ; (7) under- 

 cooling and the existence of a metastable limit ; (<s) changes of volume 

 on solidification ; ('.)) the thrust exerted by growing crystals. According 

 to Quincke's hypothesis the first step in the process of crystallization is 

 the separation of the liquid into two immiscible liquid phases. One of 

 these, present in relatively very small quantity, forms the walls of "foam- 

 cells" filled with the liquid present in greater quantity. Crystallization 

 then proceeds within the foam-cells and is largely influenced by them. 

 The crystal grain boundaries are the foam-cell walls. The author points 

 out serious objections to Quincke's foam-cell hypothesis- Attempts have 

 been made to connect the cellular structure of metals with a remarkable 

 partitioning sometimes observed in cooling liquids. This effect, visible 

 as geometrical patterns on the liquid surface, appears to be due to con- 



* Ferrum, xi. (1914) pp. 97-112 (24 figs.). 



t Proo. Roy. Soc, Series A, xc. (1914) pp. 19-25 (7 figs.). 



| Journ. Inst. Metals., xi. (1914, 1) pp. 57-118 (9 figs.). 



