360 PROCEEDINGS OF THE SOCIETY. 



•assistance towards the much-needed collection of specimens. A reply 

 was received from Sir Robert in which he generously promised to give 

 a number of specimens from his Research Laboratory, adding at the 

 same time an expression of his whole-hearted support of the scheme. 



2. The GollexUoii Itself. — After a short interval the gift of slides 

 €ame to hand. It consisted of twenty specimens, including particularly 

 interesting alloy steels, together with cast irons, and samples of varying 

 carbon content after having received different thermal treatment, 

 the whole thoroughly representative of modern metallurgical practice, 

 and affording a wide range of interesting micro-structures. The 

 specimens w^ere ground down to level surfaces, but naturally the polish- 

 ing and etching process had yet to be done. I may add that I was 

 away at a considerable distance during this period, and consequently 

 some delay was unavoidable before I was able to see the specimens and 

 consider plans for their final treatment. After I had examined the 

 specimens I approached Prof. H. C. H. Carpenter, Ph.D., F.R.S., asking 

 whether he would be so kind as to allow tlie finishing process to proceed 

 at the Royal School of Mines. To this he generously agreed, and to 

 him we are indebted for his timely assistance and interest in the 

 scheme. The sections were received back complete last July, since 

 when they have been at the Society's Rooms. 



3. Description of the more important Micro- Structures.'" — Sir Robert 

 Hadfield enclosed a detailed list, giving the chemical composition and 

 thermal treatment of each specimen, and in the light of this information 

 it may be well for me briefly to review the most interesting points of 

 the structures as seen under the microscope. 



The "Armco" iron (2148) is a beautiful specimen. It consists, 

 one might say wholly, of allotriomorphic crystals of " ferrite " (pure 

 alpha iron). The outlines of the grains are developed on etching, 

 due to minute differences of potential at their junctions. Neigh- 

 bouring grains are coloured differently owing to variations in orienta- 

 tion. The "B.B." wrought iron (2112) shows the slag-inclusions 

 very characteristic of such material. Comparison with a sample 

 of mild steel (say 1350) shows the essential difference between these 

 products. Wrought iron consists of a number of layers from between 

 which the whole of the slag has not been squeezed out. The 

 cast irons (912, 918) bring out the complexity of the constituents present, 

 the white metal being especially interesting. The low, medium, saturated, 

 and supersaturated car])on steels show the transition from a few isolated 

 islets of " pearlite " (low carbon steel) through "saturated," where the 

 whole structure is pearlitic, to " supersaturated," where areas of "cemen- 

 tite " (FcaC) make their appearance surrounding the " pearlite." The 

 *' special " steels " Era " and " Cr-Ni " are interesting, the former because 

 they alloAV of the retention of " Austenite " (solid solution of carbon or 

 FcgC in gamma iron), a constituent usually only stable at high tempe- 

 rature. The " Cr-Ni " specimens are pearlitic, as is generally the case. 



4. Preservation and Future Arrant/ements. — It remains now to deal 

 with this important matter. After careful consideration it was decided 



* See also annotated list appended to this paper. 



