December i, 1910] 



NATURE 



0/ 



contingent was predominant, including (titles omitted) 

 H. Credner, G. Giirich, K. Keilhack, A. Penck, A. Roth- 

 pletz, W. Salomon, K. Sapper, F. Wahnschaffe, and other 

 well-known names. Among those from France were 

 L. Carez, L. de Lamothe, E. de Margerie, and A. Offret ; 

 from Italy, S. CeruUi-Irelli and E. Mattirolo ; from 

 Portugal, J. Mendez-Guerreiro ; from Switzerland, M. 

 Allorge, J. Brunhes, ?nd P. Mercanton. From Denmark, 

 among others, came V. E. Hintze, \'. Madsen, and J. P. J. 

 Ravn ; from Holland, J. I. J. M. Schmutzer and Mile. A. 

 Grutterink ; from Norway, H. Reusch ; from Hungary, 

 E. de Cholnoky and E. de Maros ; and Japan was repre- 

 sented by K. Inouye and H. Yabe. Broadcast now is the 

 gathering that went with the good ship _ /Eolus on this 

 memorable voyage to Spitsbergen I 



G. W. Lamplugh. 



A FOURTH RECALESCEXCE IX STEEL. 

 TX 1868 the late Dr. George Gore, F.R.S., discovered 

 ■*• the recalescence points now known as Ar, and Ar^, 

 and in 1872 Prof. W. F. Barrett, F.R.S., discovered the 



Photo-micrograph of nearly Pure Iron containing 021 per cent. Carbon. Rapidly quenched 

 between the two peaks of Ar.i. Magnified 450 diameters. 



point Ar„ which is now known as the carbon change 

 I)oint. Prof. Barrett gave the phenomena the generic title 

 f "recalescence," by which thev have been known ever 

 -ince. 



At the recent meeting of the British .Association, Prof. 



J- O. Arnold described to the section of chemistrv 



he result of accumulated thermal and micrographic 



/oservations upon this subject extending over twenty years. 



'- "^rst described the recalescence apparatus used at 



id University, in which the tape results can be 



i either as a time-temperature or as an inverse-rate 



curve. The latter is more delicate, its coordinates being 



units of temperature and time in seconds, for units rise or 



fall in temperature. 



made possible bv a gift of chemically pure iron from Dr. 

 Hicks and Prof. O'Shea, of Sheffield University. The 

 recalescence data registered in vacuo on placing the 

 thermocouple between two small plates of this iron show 

 that the maximum of Ar, appears at 854^* C, and the 

 set-back between the two peaks of Ar, is registered at 



750° C. 



The Recalescence of Iron containing about 0-2 per cent. 

 Carbon. 

 On cooling unsaturated steels containing about 0-2 per 

 cent, carbon it was noticed that there was along the range 

 of temperature between Ar, and .\r, some thermal evolu- 

 tion which prevented the curve crossing the radiation line 

 after recalescence, and also kept it well to the right of 

 that line. Careful investigation of this phenomena re- 

 vealed the fact that whilst with iron containing 0-38 per 

 cent, carbon this new and prolonged recalescence was very 

 much augmented, as compared with a 02 per cent, carbon 

 steel, that iron containing 0-63 per cent, carbon gives out 

 during this fourth phase of recalescence much less heat 

 than the 038 per cent, carbon steel. Therefore it would 

 appear that the maximum of heat of the 

 fourth phase of recalescence is evolved from 

 a semi-saturated steel, namely, an iron con- 

 taining 0-45 per cent, carbon, and having 

 in the cold a micro-structure consisting of 

 50 per cent, ferrite and 50 per cent, pearlite. 

 The recalescence data and curves of all 

 these steels were shown on the screen and 

 minutely described. 



The Cause of the Fourth Phase of 

 Recalescence. 



By micro-thermal investigations Prof. 

 Arnold has satisfied himself that the fourth 

 phase of recalescence is due to constitutional 

 segregation, namely, the falling out between 

 -Ar, and Arj of the ferrite and hardenite 

 from their state of mutual interpenetration 

 or solid solution into microscopically in- 

 visible masses. A method was adopted for 

 rapidly quenching from nitrogen in iced 

 brine 0-2 per cent, carbon steel at various 

 temperatures. The temperatures were : — 

 (i) 995° C. (well above Ar,) ; (2) just below 

 Ar, ; (3) just after first peak of .Ar, ; (4) just 

 above Ar, ; (5) 15" (normalised or cooled in 

 air). 



The micrograph here reproduced is a 

 section quenched between the two peaks of 

 Ar,. The segregation is obvioush' proceed- 

 ing verv' quickly, and the ferrite is strongly 

 electro-negative to the dark etching areas 

 of hardenite still containing in solution 

 large quantities of iron. The micrographs 

 indicate that the critical range Ar, has no 

 influence on the segregation of hardenite 

 and ferrite. In Prof. Arnold's view these 

 five photomicrographs, when correlated with 

 the recalescence curves of the steel experi- 

 mented upon, prove that the fourth phase of 

 recalescence is due to the heat evolved 

 during the segregation of the ultimate micrographic con- 

 stituents of steel, which began at Ar, and incomplete at 

 Ar,, during the cooling of unsaturated steels at a moderate 

 rate, say 0-5° per second. 



The Recalescence of Chemically Pure Iron. 

 From many observations it appears that before even a 

 rough quantitative measurement of recalescence in steel 

 an be made it is very desirable to obtain a standard cooi- 

 ng curve of iron absolutely free from carbon ; this was 

 NO. 2144, VOL. 85] 



REPORTS ON IMPERIAL FOODSTUFFS. 



"\VrE have received No. 63 (" Gums and Resins ") and 

 No. 71 ("Foodstuffs") of the "Colonial Rejjorts : 

 Miscellaneous," comprising selected reports from the 

 Scientific and Technical Department of the Imperial 

 Institute. They refer to products, from British possessions, 

 examined at the institute with regard generally to the 

 possibility of their profitable cultivation or preparation in 

 the districts concerned. The first report is a useful little 

 monograph on gums and resins from the commercial and 

 analytical point of view, with particulars of the colonial 

 specimens examined. The chief matter of scientific interest 

 in the paper on foodstuffs, namely, a summarv of the 



