GO Mr. T. Andrews. 



to have been first initiated by Dr. H. Clifton Sorby, F.B.S., about 

 thirty years ago, and the author about the same time commenced 

 pome investigations in this direction. Strange to say, the subject 

 lias since then lain almost dormant, and only recently have scientific 

 investigators resumed the study of the ultimate microscopic struc- 

 ture of metals. Comparatively little progress has yet been made 

 in this important and fertile field of research, and our knowledge of 

 the true structure of metals is, consequently, at the present time 

 limited. Excellent work in this direction is now, however, in pro- 

 gress at the hands of several investigators, and it is hoped that by 

 means of further careful detailed observation with accurate modern 

 microscopic appliances valuable and reliable results will accrue. 



In the course of a research with high microscopical powers (includ- 

 ing 300, 500, 800, 1200, and upwards to 2000 diameters) on the micro- 

 crystalline structure of large masses of wrought iron, the author had 

 the privilege recently to observe the following novel metallurgical 

 facts. 



When large masses, several tons in weight, of practically pure 

 wrought iron were allowed to slowly cool from a white heat, a 

 secondary or subcrysballisation of the metallic iron occurred. The 

 normal primary crystals of the iron, or those which have hitherto 

 been regarded as constituting the ultimate structure of the metal, 

 were found to inclose a subcrystalline formation consisting of very 

 minute, and much smaller, crystals of pure iron also belonging to the 

 regular order of crystallisation. These crystals sometimes manifested 

 the hexagonal form, the predominant angle being about 120, and 

 often they assumed the form of simple cubes. The secondary 

 crystals were contained within the area of the larger primary 

 crystals. 



Typical illustrations of this duplex crystallisation found in two 

 large iron forgings are given in figs. 1 and 2, and the relative 

 dimensions of a number of individual crystals are given on Tables I 

 and II. 



The results of twenty measurements of the primary crystals and 

 twenty measurements of the secondary crystals taken on each forg- 

 ing are given on these tables. 



The markings of the intercrystalline spaces or junctions of the 

 secondary crystals were very clearly defined, but they were 

 exceedingly minute. The general form, contour, and relative size 

 of the primary and secondary crystals, as seen in section, will be 

 noticed on reference to the accurate tracings, figs. 1 and 2. 



Judging roughly from the indications of the average micro- 

 measurements on Tables I and II, there would appear to be approxi- 

 mately 1,000,000,000 of the secondary crystals in a cubic inch of the 

 metallic iron. 



