234 



NATURE 



[November 21, 1918 



THE OCCLUSION OF GASES IN METALS. 



ON Tuesday, November 12, the Faraday Society 

 held a discussion on the above subject, attended 

 In a very representative gathering of the various 

 aspects of it, theoretical and experimental. After a 

 foreword by the president, Sir R. Iladfield, on the 

 great war, the discussion was opened by Profs 

 Alfred W. Porter, who emphasised that the terra 

 "occlusion" includes, in reality, a number of pheno- 

 mena : chemical combination, simple or compound 

 solid solution, surface adsorption accompanying solu- 

 tion, surface condensation unaccompanied b\ dilu- 

 tion, and inclusion of gas forming blowholes visible to 

 tbr naked eye or microscope. The difficulty of dis- 

 tinguishing between these several types was illustrated 

 by the case of the occlusion of hydrogen bv palladium, 

 the nature of which, even at the present dav, is ^t i 1 1 

 an unsettled problem. Amongst phenomena due to 

 occlusion are the passivity of iron and the associated 

 fact of the embrittling of iron bv caustic soda. But 

 there are other phenomena of more theoretical 

 interest, such as the Volta effect, which has often been 

 attributed to condensed layers of gases. By the ex- 

 periments of O. W. Richardson and of Langmuir on 

 thermionic emissivity, the question of the origin of 

 the Volta effect has been completely reopened. 



In connection with the brittleness associated with 

 occlusion in iron and other metals, the opener en- 

 deavoured to elicit an expression of opinion as to the 

 nature of brittleness, illustrating his remarks with the 

 well-known behaviour of cobbler's wax, which is ex- 

 ceedingly plastic under the action of small forces of 

 long duration, but is as brittle as glass when struck a 

 sharp blow. lie laid stress on the necessity for paying 

 attention to the lime element in specifying brittleness. 



Mr. Cosmo Johns followed on the technical side 

 with a paper on the properties of metals as affected by 

 their occluded gases. He distinguished between gases 

 which are absorbed as surh and those which are 

 formed as a result of reactions between non-gaseous 

 constituents during the cooling of the metals in ques- 

 tion. It is known that molten copper and iron dis- 

 solve more hydrogen than when those metals are 

 solid. A molten mass saturated with hvdrogen at a 

 particular partial pressure will, during freezing, 

 become supersaturated with the gas. Some of this 

 must be entrapped between the growing crystals and 

 exist as macroscopic or microscopic gas enclosures, 

 though this is probably not the only method bv which 

 occlusion occurs. Probably it is the inter-crvstalline, 

 amorphous matter that is chieflv concerned, and 

 brittleness will be due to the change in this produced 

 by the gas. He attributed the CO. and CO occluded 

 to reactions between dissolved oxide of iron and the 

 carbon in the steel at the particular temperature when 

 iron oxide, being thrown out of solution as freezing 

 progresses, becomes concentrated in the mother-liquor 

 between the growing crystals and reacts with the 

 carbon which has not suffered the same concentration. 

 He urged that all our knowledge of the properties of 

 metals merely relates to metals containing occluded 

 gases, and not to pure metals themselves. 



Dr. Thomas Raker gave a description of experi- 

 ments made to discover the relation, if any, between 

 the temperature of evolution of gas and the critical 

 points of steel. He finds that with hard steels the 

 evolution of hydrogen reaches a maximum rate at 

 6oo° C, and below this temperature constitutes the 

 greater part of the gas given off. Carbon monoxide 

 is slowly evolved from the beginning, and reaches its 

 maximum rate at 688° C. With soft steel there is a 

 further point of maximum evolution of hydrogen and 

 carbon monoxide at 786 C. 



NO. 2560, VOL. I02] 



Dr. McCance spoke on the balanced reactions in 

 steel manufacture, particularly with reference to the 

 open-hearth process. Dr. Hatfield pointed out the 

 large influence which silicon has upon occlusion. 



Dr. Rosenhain emphasised that all liquids are 

 brittle, but, as the opener afterwards pointed out, 

 it would be better to say all bodies. Mr. ('. V. Boys, 

 refening to the spitting of silver on solidification, 

 stated that he had found that to avoid loss of silver 

 through spitting in cupellation it was necessary to 

 cool it very slowly; and he asked if this was due to 

 the evolution taking place over a range of tempera- 

 ture, and not all precisely at the solidification point. 

 It could not be due to differences of temperatun in 

 the solidifying mass, because a considerable amount 

 of undercooling takes place, and the solidification, 

 when it occurs, is a very rapid process, the whole mass 

 rising practically instantaneously to the melting- 

 point . 



Sir T. K. Rose dealt with the bearing of Le 

 Chatelier's principle upon the change of the concen- 

 tration of dissolved gases with temperature. Prof. 

 N. T. M. Wilsmore pointed out that he had recently 

 observed that the diminution of solubility of gases 

 with rise of temperature, so far as data go, is 

 peculiar to water as solvent, and that, even in the 

 case of water, there seems to be a minimum at a 

 moderate temperature (see the data in the last edition 

 of Landolt-Bornstein). This important observation is 

 quite contrary to the belief usually held. The excep- 

 tional character of water mav be attributed to the 

 variation in its degree of association. 



Prof. H. E. Armstrong laid stress on the artificiality 

 of distinguishing dissolution from combination ; dis- 

 solution is combination. 



Dr. R. E. Slade directed attention to the bearing of 

 the eutectic point of Ag — Ag,0 at about 6° below the 

 melting-point of silver; and Drs. Darker and Ravner 

 described interesting experiments with very large 

 masses of molten silver. 



Dr. Gwyerwas in doubt as to the reason for the pro- 

 portionality of solubility in some cases to the square 

 root of the pressure, apparently omitting to notice the 

 bearing of the Nernst-van't Hoff law of distribution 

 when the molecular association is different in the free 

 and dissolved states. 



Manv other interesting points were made by various 

 speakers. The openers reserved their detailed replies 

 to the printed discussion, where these points will be 

 dealt with. 



GEOLOGY OF THE PERSIAN OILFIELDS. 



AN interesting paper on the geology of the Persian 

 oilfields by Messrs. H. G. Busk and H. T. 

 Mayo was read at the meeting of the Institution of 

 Petroleum Technologists on October 15. Three areas 

 are treated : the Bakhtiari country, in which the only 

 oilfield worked as yet is situated; the Aluvaz-Pusht-i- 

 Kuh country; and the Qishm Island and Persian 

 Gulf region. The first of these is described in most 

 detail. The rocks are divided into three series 1 The 

 Asmari, Eo-cretaceous, at the base consists of massive 

 limestones 2000 ft. or more in thickness. It is suc- 

 ceeded bv the Miocene Fars series, more than 7000 ft. 

 thick, divided into three groups : the lower, formed 

 of some 3500 ft. of massive gypsum, shales, rlavs, and 

 intercalated beds of detrital limestone; the middle, 

 1000 ft. of clavs, shales, intercalated gypsum, lime- 

 stone, and sandstone; and the upper, 2700 ft. of 

 clays, shales, and intercalated red and brown sand- 

 stones. The Fars series is overlaid bv the Bakhtiari 

 series of Pliocene age, of which the lower group, 



