1904.] Properties of the Alloys of Silver and Cadmium. 



The silver- cadmium standard alloy is more ductile and is whiter 

 than the corresponding alloy of silver and copper, which has a slightly 

 yellowish tinge. The ingots obtained were 21 '5 cm. long, 15'3 cm. 

 wide and 1'25 cm. thick. They were rolled to a gauge of 1'25 mm. 

 and pieces cut from all parts were assayed, with the results that the 

 plates* 'were found to be practically of uniform composition. The 

 cadmium does not interfere with the ordinary methods of assay, no 

 difference in results due to interference being observable when the 

 trial-plates were compared with pure silver by the Gay-Lussac and 

 Volhard processes of assay. In practice when the fineness of a silver- 

 copper alloy is being compared with that of the trial-plate, by means of 

 the Volhard process, the nitric acid solution of the copper alloy would 

 be coloured blue, while that of the cadmium alloy would remain 

 colourless. This would interfere with the correctness of the com- 

 parative final readings, but in order to avoid this difficulty, it is 

 sufficient to add a piece of copper of the appropriate weight to the 

 solution of the cadmium alloy. Wlien the silver-cadmium alloy is 

 cupelled, the cadmium burns off' and the loss of silver is about four 

 parts in 10,000 more than if the alloying metal were copper. In com- 

 parisons by the cupellation process, it is, therefore, essential that the 

 assay pieces should be made of similar composition by suitable additions 

 of base metals. This course presents no difficulty and in no way 

 detracts from the value of the trial. 



The results of these experiments show that trustworthy and con- 

 venient trial-plates can be made of silver and cadmium, but it 

 remained to be determined by further study of the properties of the 

 series of alloys whether the uniformity in composition of the trial-plates 

 was fortuitous, or whether it was the inevitable result of its 

 constitution. 



The silver-cadmium series has been investigated by Gautier,f who 

 stated that the freezing-point curve consisted of two parts meeting at 

 a point corresponding to the alloy containing about 42 per cent, of 

 silver and that the alloys appeared to consist of isomorphous mixtures 

 of a compound of silver and cadmium with one or other of the pure 

 metals. In order to confirm these observations of Gautier a number 

 of alloys, consisting of silver and cadmium, were prepared and analysed. 

 The silver used for this purpose was purified with the precautions 

 adopted in the preparation of fine "proof" silver in the Mint and was 

 1000 fine. The cadmium was purchased as pure and was examined for 

 impurities, but none were detected. The proportion of silver in the 



* One of the plates was sent to Mr. F. W. Harrold, the Assay Master at the 

 Goldsmith's Hall, and another to Mr. H. Westwood, one of the Assay Masters of 

 the Assay Office, Birmingham. They have kindly made a number of assays on the 

 plates, and state that the composition of each plate is uniform. 



t 'Bull, de la Soc. d' Encouragement,' Fifth Series, I, p. 1315 (1896). 



