ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 99 



and historical aspects. Among these may be mentioned ' Bacteriology 

 of Plague,' by Mr. D. C. Rees, and ' Methods of making Antitoxic and 

 Preventive Fluids,' by Dr. C. B. Stewart. 



Progress in Metallography.* — T. K. Rose treats this subject with 

 special reference to Le Chatelier's suggestions in the Bulletin de la 

 Societe a" Encouragement for September last. These relate mainly to the 

 best methods of obtaining graduated polishing powders, of illumination, 

 and of making alloys. In examining the alloys of two metals, much 

 time is consumed in making and suitably preparing a series of typical 

 specimens. Le Chatelier proposes to shorten the search by melting to- 

 gether two superimposed layers, each consisting of a pure metal, the 

 lighter one being on the top. If no alloys are formed of greater density 

 than the heavier metal, and the crucible is allowed to cool undisturbed, 

 a culot can be obtained which, oh being sawn through vertically, shows 

 a complete graduation from one pure metal to the other, passing through 

 the whole series of alloys, which can then be studied in one specimen. 

 Figures are given of the aluminium-copper series obtained in this way. 



Crystalline Structure of Iron and Steel.f — J. E. Stead describes 

 an elaborate investigation of this subject. He arrives at ten conclusions, 

 of which the following is a condensed summary : — 



(1) That granules and crystals should not be confused ; for although 

 a granule is built up of crystals, its external form is not that of any kind 

 of crystal, as it takes its shape from its surroundings. It is better to 

 replace the term granule by grain. 



(2) That grains formed in the solidification of liquid metals are 

 large or small, according to whether the freezing is rapid or slow. 



(3) That in practically carbonless pure irons, and in steels of fine 

 grain produced by either forging or certain heat treatment, the grains 

 increase in size slowly at 500° C, and more rapidly at between 600° and 

 750° C. ; and it is possible, by heating at about 700° for a few hours, to 

 develope granular masses of exceeding coarseness. When pure iron made 

 coarsely granular by long heating at a dull red heat is heated between 

 750° and 870°, as a rule the structure is not materially altered ; but 

 at 900° the granules again become small, and heating to 1200° C. does 

 not apparently produce any difference in their dimensions. 



(4) That when steels containing 0*20 to 1-20 p.c. of carbon are sub- 

 ject to prolonged heating at 700° C, the grains do not increase in size ; 

 but they do increase if the temperature is raised above 750°. When, 

 however, this coarse steel is reheated to between 700° and 750°, the 

 coarse structure vanishes and the grains become very fine. 



(5) That in steels with 0-10 to 0-15 p.c. containing the pearlite in 

 widely separated areas, on heating and quenching from 750°, the large 

 ferrite grains are not broken up, and the carbon apparently does not 

 expand or diffuse beyond the original areas, as previously demonstrated 

 both by Osmond and Arnold ; yet, when the heating is raised to near 

 850° and the steel allowed to cool down naturally, the carbon areas are 

 found far beyond their original positions, and exist in a number of 

 smaller segregations. 



* Nature. Jan. 3, 1901, pp. 232-3 (3 fisrs.). 



t Metallo^raphist, Oct. 1898, pp. 289-341 (26 Hers, nn.l 3 diagrams). 



II 2 



