NA TURE 



[June 23, 1904. 



deposited, and the remainder froze as a eutectic in which 

 these crystals were encased. The phosphide crystals showed 

 sharp geometrical outlines, in marl<ed contrast to the out- 

 lines of the crystals of solution, because the phosphide was 

 deposited as a' definite constituent in which the other con- 

 iatuent (iron) was not soluble. 



To explain the zebra markings characteristic of eutectics, 

 Dr. Ewing briefly referred to the phenomenon of surfusion, 

 and gave it as his opinion that the formation of a eutectic 

 occurred by alternate surfusion or supersaturation of each 

 constituent in the other. A eutectic in the fluid state and 

 about to freeze might be defined as a saturated solution of 

 A in B which was at the same time a saturated solution 

 of B in A. On the temperature falling, an alternating 

 condition of instability results. By surfusion, A is at first 

 supersaturated with B, until some of B is thrown dow^n, 

 leaving, in the liquid that remains, B supersaturated with K. 

 Consequentlv, some of A is in turn thrown down, and so 

 on alternately. In the appearance of a eutectic alloy there 

 was much that was suggestive of alternate deposit of the 

 two constituents, and it was in some such way as this that 

 Dr. Ewing conceived the alternation to take place. 



Eutectics in which the constituents were not of the same 

 crystalline system appeared to be mechanically weak. A 

 very small quantity of bismuth added to copper or silver or 

 lead was shown by Arnold to produce great brittleness, 

 owing to the weakness of the cement which the eutectic 

 formed in the joints between the grains, although the 

 individual grains themselves preserved their original 

 malleability. In other eutectics no such weakness, as a 

 rule, was found, and the intergranular cement was as strong 

 as the grains themselves— often, indeed, it was distinctly 

 stronger. 



From the engineering point of view, by far the most im- 

 portant allovs were those in which the chief constituents were 

 iron and carbon, or rather iron and carbide of iron. By help 

 of Roozeboom's diagram, the lecturer explained briefly the 

 characteristics of high and low carbon steels, and the trans- 

 formations which occur in the process of cooling at tempera- 

 tures far below that at which the metal becomes wholly 

 solid which had formed the subject of much study by 

 Osmond, Roberts-Austen, and others. By the process of 

 quenching these changes might be to some extent arrested, 

 and the mechanical properties secured which characterise 

 hardened steels. The evolution of heat in the transform- 

 ation was illustrated bv means of cooling curves, and by 

 experiments in which steel wire was allowed to cool after 

 being electricallv heated above the transformation points. 

 While passing through the region in which transformation 

 occurs, the steel is specially plastic ; this was illustrated m 

 the cooling from bright redness of a steel wire coiled into 

 the form of a spring and carrying a light weight. The 

 spring extended in a conspicuous way while the process of 

 re-crystallisation associated with " recalescence " was going 

 on. The phenomenon of recalescence was further illustrated 

 in an automatic record obtained during the lecture with 

 a Callendar recorder which was exhibited by the Cam- 

 bridge Instrument Company. The recent results of 

 Carpenter and Keeling, in their research at the National 

 Physical Laboratory, were referred to as giving in most 

 particulars a general confirmation of Roozeboom's views. 

 Other examples of transformation occurring in the_ solid 

 state were illustrated by photographs selected from Neville 

 and Heycock's series for the copper-tin alloys. 



The gradual changes of structure which go on even at 

 atmospheric temperatures in lead and other metals after 

 the structure has been broken up by severe straining were 

 next described, photographs by Rosenhain and the lecturer 

 being exhibited to demonstrate the progressive character 

 of these changes, and the manner in which they would be 

 accelerated bv elevating the temperature. 



In conclusion, the lecturer referred to the analogous case 

 of glacier ice. It had for long been known to possess a 

 granular structure, and each grain was a crystal just as 

 in the case of metals. Photographs by Principal Skinner, 

 illustrating this granular structure, were shown. In the 

 upper n^v<5 the grains were vague and comparatively small ; 

 as the glacier slowly travelled down the grains became 

 consolidated and large, and their outlines became well de- 

 fined. It was clear that a slow process of crystal growth 

 was going on, and in the lecturer's opinion it was to this 



NO. I 808. vni.. 70I 



very process of growth that the plasticity of the glacier as 

 a whole was to be ascribed. How^ ice came to be plastic in 

 large masses was a question to which physicists had 

 suggested more than one answer. But the plasticity was. 

 intelligible enough when one realised that the whole mass 

 was in the act of structural change. Just as the spiral 

 spring in the experiment with steel showed during its 

 transformation a special plasticity, so the glacier showed 

 a general plasticity throughout its course, inasmuch as it 

 was undergoing a slow and probably continuous structural 

 change in the crystallisation of its individual grains. -Alike 

 in the metal and the ice, nature was apparently following 

 one structural process, and the consequences as to plasticity 

 were alike in both. In neither case was any constancy to 

 be found save the constancy of change. Nothing was more 

 striking to a worker in this field than the evidence he found 

 that those substances on which we were most accustomed 

 to relv as constant were undergoing, sometimes compara- 

 tively fast and sometimes very slowly, a process of internal 

 flux. A monument more enduring than brass might be 

 a lofty ideal, but it was seen at least to be an ideal easy 

 of conception when one realised how far from constant the 

 inner structure of brass and other metals was apt to be. 



THE GAS SUPPLY OF THE METROPOLIS. 

 A committee was appointed by the Board of Trade ire 

 ■'^ January last to inquire and report as to the statutory 

 requirements relating to the illuminating power and purity 

 of the gas supplied by the metropolitan gas companies, and 

 as to the methods now adopted for testing. The report of 

 this committee has now been presented, after hearing 

 evidence from the metropolitan gas referees, from repre- 

 sentatives of the London County Council, the Corporation 

 of the City of London, and each of the three gas .companies 

 concerned. 



The supply of gas in the metropolis being a monopoly, 

 provision is made in the private Acts of the various com- 

 panies for securing the maintenance of certain standards 

 of purity and illuminating power. Three gas referees are 

 appointed by the Board of Trade, with power to prescribe 

 and certify the situation and number of testing places to 

 be provided, and to lay down the conditions under which 

 the testings are to be made. By the insertion of clauses 

 in recent Acts obtained by the gas companies bearing on 

 the mode of testing, these powers have been somewhat 

 curtailed. The testing places are usually fitted up in houses 

 owned or leased by the gas companies, the tests being made 

 by oflicials appointed by the controlling authority, either 

 the London County Council or the Corporation of the City 

 of London. A comparison of the tests made at the official 

 stations with tests made with a portable photometer in the 

 neighbourhood of those stations having shown considerable 

 discrepancies, attempts have been made by the controlling 

 authority to legalise the portable photometer, but these 

 attempts have been successfully resisted by the gas com- 

 panies before Parliament, and the present committee in 

 the report is not prepared to recommend the adoption of 

 such tests. As, however, these results have given rise to 

 doubt as to whether the gas supplied to the testing stations 

 really represents the gas supplied to the public, the gas 

 referees have laid down a requirement that the gas to be 

 tested is to be biought direct from the main to the testing: 

 place by a single service pipe, without tap or branch or 

 provision for connection of any kind outside the testing 

 place. This has been strenuously resisted by one of the 

 companies, and has led to the curious result that, although 

 the referees have powers to prescribe testing places, they 

 have no powers to enforce their prescription, and owing to 

 the deadlock thus created two testing places have remained 

 closed for some years. 



The committee is of opinion that this requirement is a 

 reasonable one, and that it might with advantage be made 

 a statutorv requirement not dependent on the prescriptiorp 

 of the gas referees. 



In the case of any deficiencies being found by the officiaF 

 examiners, action is taken by the controlling authority 

 before a magistrate, with a view to the recovery of the 

 forfeitures specified in the Acts. If any technical objection 

 is raised by the gas companies, the question is referred to 



