52 SECTIONAL ADDRESSES. 



of structure.' The methods described by Sorby for pohshing and 

 etching alloys and his method of vertical illumination (afteinvards 

 improved by Beck) are employed to-day by all who work at this branch 

 of metallography. 



The lantern-slides, now shown, were reproduced from his original 

 photographs; they form a lasting memorial to his skill aa an investi- 

 gator and his ability as a manipulator. In 1887 Dr. Sorby published 

 a paper on the microscopical structure of iron and steel in the Journal 

 of the Iron and Steel Institute. This masterpiece of clear writing 

 and expression, even with our present knowledge, needs but little 

 emendation. In this paper he describes Free Iron (feiTite) carbon as 

 graphite, the pearly constituent as a very fine laminar structure (pearlitic 

 structure), combined iron as the chief constituent of white cast iron 

 (cementite), slag inclusions, effect of tempering steel, effect of working 

 iron and steel, cementation of wrought iron, and the decarbonisation 

 of cast iron by haematite. A truly remarkable achievement for one 

 man. 



From 1854-68 Mattheisen published in the Eeports of the British 

 Association and in the Proceedings and Transactions of the Eoyal 

 Society, a large number of papera on the electrical conductivity, 

 tenacity, and specific gravity of pure metals and alloys. He concluded 

 that alloys are either mixtures of definite chemical compounds with an 

 excess of one or other metal, or solutions of the definite alloy in the 

 excess of one of the metals employed, forming, in their solid condition, 

 what he called a solidified solution. This idea of a solidified solution 

 has developed into a most fruitful theory upon which much of our 

 modern notions of alloys depends. Although, at the time, the experi- 

 ments on the electrical conductivity did not lead to very definite con- 

 clusions, the method has since been used with great success in testing 

 for the presence of minute quantities of impurities in the copper used 

 for conductors. 



In the Philosophical Magazine for 1875, F. Guthrie, in a 

 remarkable paper, quite unconnected with alloys, gave an account of 

 his experiments on salt solutions and attached water. He was led to 

 undertake this work by a consideration of a paper by Dr. J. Eea, the 

 Arctic explorer, on the comparative saltness of freshly formed and of 

 older ice floes. Guthrie showed that the freezing-point of solutions was 

 continuously diminished as the percentage of common salt increased, 

 and that this lowering increased up to 23.6 per cent, of salt, when the 

 solution solidified as a whole at about 22° C. He further showed, 

 and this is of great importance, that the substance which first separated 

 from solutions more dilute than 23.6 was pure ice. To the sulDstance 

 which froze as a whole, giving crystals of the same composition as the 

 mother liquor, he gave the name cryohydrate. At the time he thought 

 that the cryohydrate of salt containing 23.6 per cent. NaCl and 76.4 per 

 cent, of water was a chemical compound 2NaC1.21H20. In suc- 

 ceeding years he showed that a large number of other salts gave solu- 

 tions which behaved in a similar manner to common salt. He 

 abandoned the idea that the cryohydrates were chemical compounds. 



How clear his views were will be seen by quotations from his 



