November 4, 1897] 



NATURE 



1 1 



sidered at the Congress without reference to the papers 

 on domestic economy. It must be admitted that the 

 teaching of such subjects as cookery and laundry work 

 'has been made of late years distinctly more educative, 

 and at the same time more practically useful. Much of 

 this improvement is undoubtedly due to the educational 

 experiments carried out by Mr. Hugh Gordon and by 

 Mr. Heller, under the direction of the London School 

 Board. The results of their work may be seen in the 

 training schools attached to some of the polytechnics, 

 and in the classes held in other institutions. Miss 

 Walter's paper on " Domestic science as an element in 

 girls' education " shows the great advance that has 

 recently been made in the treatment of this important 

 subject, and ■ marks • the distinction, not always clearly 

 indicated, between the teaching of domestic science and 

 of domestic arts. For persons quaUfied to give instruc- 

 tion in the science there is an increasing demand ; and 

 in her paper. Miss Walter gives an outline of the course 

 of training such persons should undergo, and her sugges- 

 tions do not err on the side of incompleteness. 



It is doubtful whether the bulky volume, the contents 

 of which we have endeavoured to summarise, will be read 

 by many, even of those persons who are actually engaged 

 in the work of technical education. Such congresses, 

 however, serve a useful purpose in bringing people 

 together for the interchange of opinion, and in inducing 

 a few persons to think seriously on some of the difficulties 

 which, owing to its wide meaning and the variety of its 

 methods, the problems of technical education undoubtedly 

 involve. 



MICROSCOPIC STUDY OF ALLOYS. 



T^HE study of metals with the microscope proceeds 

 ■*■ apace, and is now becoming as generally pur- 

 sued among metallurgists as the determination of 

 melting points has been during the last five years. 

 Since the appearance of Prof Roberts-Austen's article 

 on " Micrographic Analysis" (Nature, vol. Hi. p. 367, 

 1895) of iron and steel, a large amount of work has been 

 done ; but most observ^ers still devote themselves more or 

 less exclusively to the study of this metal, attacking 

 unsolved problems which seem to have great industrial 

 importance. This tendency is unfortunate from some 

 points of view, for the complex constitution met with in 

 that protean element makes it less easy to explain the 

 observed appearances until, by work on simpler alloys, a 

 better acquaintance with the whole subject has been 

 obtained. M. Charpy is one of those who has resisted 

 the temptation offered by the alloys of industry, and in a 

 recent paper ^ has given some interesting results of his 

 investigations on binary alloys which are well worth 

 re-statement. 



It is now fairly established that microscopic examina- 

 tion gives an immediate analysis of alloys, which is all 

 the more valuable for differing in its results from chem- 

 ical analysis, since these differences indicate the exist- 

 ence of definite compounds, and elucidate the structure 

 in other ways. The immediate analysis is now made 

 with the aid of a planimeter, as Sauveur recommended, 

 by which the ratio of the areas occupied in the micro- 

 scopic field by the various constituents can be measured. 

 The metal or metals forming each of these constituents 

 can often be indicated by their colour, hardness and, 

 above all, the effects on them of various reagents, and 

 thus a full account of the alloy can be given. 



In the normal type of constitution of binary alloys, 

 crystals of one of the metals, or of a definite compound 

 of the two, are seen enveloped in a second constituent, 

 which is generally the eutectic alloy, containing both 



1 " Etude Microscopique des Alliages Mitalliques. Bull, de la Soc. 

 d Encouragement, vol. ii. (1897), p. 384. 



NO. 14.62. VOL. 57] 



elements in a very finely-divided state. The compo- 

 sition of the eutectic mixture remains constant, whilst 

 the amount of isolated crystals varies with the percen- 

 tage composition of the alloy. The limiting cases of a 

 pure definite compound or metal, and of a pure eutectic 

 mixture may be grouped with these alloys. 



Eutectic alloys vary in appearance according as they 

 have been cooled slowly or quickly. In the latter case, 

 the surface is uniformly striated, but the crystals or 

 crystallites are so small, that it is difficult to obtain 

 satisfactory photographs of them. When the solidifi- 



FiG. I. — Alloy of silver, 66 per cent. ; antimony, 34 per cent. 



cation is slow, however, the separation into lamellae is- 

 strongly marked, especially when viewed under high 

 powers, and this structure is highly characteristic of 

 eutectic alloys, being easily traced in any of them what- 

 ever the metals in the alloy may be. It is well shown in 

 Fig. I, which represents an alloy containing silver 66 per 

 cent., antimony 34 per cent., magnified 500 times ; the 

 metal has been treated with sulphuretted hydrogen, which 

 has blackened the silver and left the antimonv unchanged. 



Fig. 2. — Alloy of tin, 90 per cent. ; antimony, 10 per cent. 



In the same figure some straight edges can be seen, in 

 which the ramifications end, and which sketch out shapes 

 resembling those of crystals of antimony. The presence 

 of these crystallites or incipient crystals in eutectics con- 

 stitutes one of the resemblances between them and the 

 micro-felsitic basis observed in many igneous rocks, and 

 it seems likely enough that if light transmitted through 

 these alloys could be examined, it would show that they 

 are on the borderland between crystalline and amorphous 

 matter. 



