OF METALS CONS I DKHKD IN RELATION* TO THE PERIODIC LAW. 341 



or by the presence of occluded gases : it possesses considerable ductility and tenacity ; 

 and the amount of the metallic or other impurity added to the precious metal can be 

 determined with rigorous accuracy. With the exception of iron, gold has received 

 more attention than any other metal in relation to the effects of impurities upon it, 

 and much information upon the subject is scattered through the works of the older 

 chemists ; but the first systematic experiments were made, by the direction of 

 the Lords of the Committee of Privy Council, by Mr. HATCHETT in 1803, who 

 endeavoured to ascertain " the chemical effects produced on gold by different metallic 

 substances when employed in certain proportions as alloys." He obtained results of 

 great interest, which were communicated to the Royal Society* ; but in his time the 

 importance of submitting metals to mechanical tests was not appreciated ; his 

 observations were thus mainly directed to ascertaining whether gold is rendered hard 

 and brittle by the presence of foreign metals. The gold he employed was only of 

 commercial purity, and he specially examined the effect of impurities on the standard 

 gold used for coinage, which contains 916'7 parts of pure gold and 83 '3 of copper per 

 1000 parts. He showed, by means of bending and hammering the gold, that small 

 quantities of certain metals render it very brittle, and he concluded that " the 

 different metallic substances which have been employed in the present experiments 

 appear to affect gold nearly in the following decreasing order : 



1. Bismuth. 



2. Lead. > These are nearly equal in effect. 



3. Antimony. 



4. Arsenic. 



5. Zinc. 



6. Cobalt. 



7. Manganese. 



8. Nickel. 



9. Tin. 



10. Iron. 



11. Platinum. 



12. Copper. 



13. Silver." 



In 1886, in a lecture delivered at the Royal Institution.t I pointed out that 

 standard gold breaks with a load of 18 tons to the square inch, and elongates 34 per 

 cent, before breaking. If the standard gold has only ao * o6 th part of lead added to it, 

 it becomes very fragile, and breaks, as is indicated by the following diagram, with a 

 stress of about 5 tons to the square inch, instead of the 18 tons borne originally. 

 It is remarkable that -r^oth part of lead added to gold does not appear to diminish 



' Phil. Trans.,' 1803, Part 1, p. 43. 



t RoBKBTS-AcsTKN, ' Roy. Inst. Proc.,' 1886 ; and ' Engineering,' May 28, 1886. 



