ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 119 



were the Sclerometer, using a weighted diamond point, general applica- 

 tion, the method of Brunei for mild steel and similar materials, and 

 the drilling test of Keep for cast iron. In conclusion, the lecturer 

 emphasised the necessity for greater attention to the quantitative deter- 

 mination of the relative hardness of metallurgical products on account 

 of the enormous differences in the usefulness and length and life of tools, 

 nails, tires, and numberless other articles, due to what might at first 

 ■sight appear to be unimportant differences of hardness. 



Possible non-brittleness of Steel under certain conditions.* — C. 

 Fremont points out that the general opinion as to all steels and irons, 

 whatever their quality, becoming brittle in consequence of a permanent 

 deformation effected statically or by shock between 200° and 450° C, is 

 only a hypothesis. He quotes experiments to show r that Denain steel, 

 used for the boilers of locomotives on the West of France Railway, is an 

 exception. Hence he concludes that the usual brittleness is not an 

 inherent property of the metals, but is a defect capable of being overcome 

 by suitable conditions of manufacture. 



Certain Properties of Alloys of Silver and Cadmium.f — The varia- 

 bility in composition of silver-copper alloys has always been a difficulty 

 in questions of trial plates for coinage and silversmiths' work. Samples 

 taken from the corners and centre of the same ingot will, even under 

 the most favourable circumstances, show a difference in composition of 

 1*2 per 1000, or sometimes more. T. K. Rose has found that trust- 

 worthy and convenient trial-plates can be made of silver and cadmium. 

 His investigations included a study of the microstructure from which 

 he concludes : (1) That evidence is afforded of the existence of the 

 compounds AgCd 3 , Ag 2 Cd 3 , AgCd, Ag 3 Cd 2 , Ag 2 Cd, and Ag 4 Cd ; (2) That 

 the alloys containing from 0-25 p.c. of silver consist, when solid, of 

 crystals of AgCd 3 set in a matrix of cadmium. Those containing 

 between 25 and 10 p.c. of silver consist of the compound Ag 2 Cd 3 set 

 in a matrix consisting mainly of AgCd 3 . The alloy containing about 

 50 p.c. of silver consists of crystals of a silver-rich body set in a matrix 

 consisting 'chiefly of AgCd 3 . The matrix or eutectic solidifies at 420°, 

 or nearly 300° O. below the freezing point of the crystals. The alloys 

 containing from 50-60 p.c. of silver consists, at temperatures above 

 420° C, of mixtures of two different solid solutions, one of which is 

 chiefly composed of the compound AgCd, and the other of Ag 3 Cd 2 . 

 Traces of the eutectic freezing at 420° C. are still visible. When more 

 than 80 p.c. of silver is present, the alloys consist of a mixture of two 

 bodies at temperatures between the liquidus and solidus curves, but these 

 unite to form a single solid solution at points on the solidus curve ; 

 (3) That the alloys containing over 80 p.c. of silver do not undergo 

 segregation under ordinary conditions, and are practically homogeneous 

 and uniform in composition. They are well suited as a material for the 

 manufacture of trial-plates. 



* Comptes Renrius, exxxix. (1900) pp. 1032-3. \ 



t lVoc. Roy. Soc.,lxxiv. (1904) pp. 218-30 (8 figs.). J 



