638 SUMMARY OF QUERENT RESEARCHES, 



iron and of other decarburized specimens showed peculiar streamers 

 of ferrite running from the edge to the centre. By insert- 

 ing a length of solid carbon in the hot part of the furnace this 

 decarburizing action was avoided. The degree of carburization was 

 found to increase with increase of rate of flow of gas, temperature and 

 pressure. A sudden increase in the amount of carbon absorbed 

 occurred between 890° and 900°, which is considered to correspond with 

 the beta-gamma allotropic change in pure iron. There is a limiting 

 temperature between 710° and 810° below which carburization will not 

 occur. The effect of pressure holds up to a critical value (which varies 

 with the temperature) beyond which increase of pressure has very little 

 effect. The character of the cemented cases does not conform to the 

 prevailing view that hydrocarbons give cases high in ceraentite. With 

 atmospheric pressure the carbon-content of the case did not exceed the 

 eutectoid ratio under any conditions, and hypereutectoid layers in the 

 case were only obtained by the use of high pressures. Several photo- 

 micrographs are given illustratiug the character and depth of cemented 

 cases produced under different conditions. 



Influence of Surface-tension on the Properties of Metals.""' — A 

 further account ■ is given by F. C. Thompson of the theory of the 

 existence of surface-tension forces operating in metals at the junctions 

 between the crystals and the inter-crystalline films of amorphous modifica- 

 tion. The author also replies to criticism of the views previously put 

 forward. Analogies are drawn from the phenomena noted with metallic 

 crystals in the presence of the liquid metal. The rounding of the angles 

 of dendrites of metals, such as lead and tin, withdrawn from the residual 

 liquor during solidification, is attributed to similar surface-tension forces 

 acting between the liquid amorphous condition and the solid crystalline 

 condition. Explanations are given, based on the theory, of the structural 

 re-arrangements which follow the annealing of plastically deformed 

 ferrite and of other phenomena. Surface-tension forces are at work in the 

 granulation of pearlite produced by long annealing of high carbon steels 

 at temperatures of about 650" C, as an examination of structures inter- 

 mediate between the lamellar and spheroidal forms shows that the carbide 

 plates break up into drops before coalescence occurs. 



* Journ. Iron and Steel Inst., xcv. (1917, 1) pp. 155-74 (7 figs.). 



