On Certain Properties of the Alloys of the Gold-Copper Series. Ill 



plate, which contains 91 '6 per cent, of gold and 8'3 per cent, of copper. 

 This alloy was cast into flat bars of various dimensions, and assays 

 were made on pieces cut from all parts of the plates into which the bars 

 were rolled, care being taken to adopt all the precautions described by 

 one of us with a view to ensuring accuracy in the determinations.* 

 This enabled the limit of error to be reduced to 0*02 per 1000 on a 

 mean of three assays. In all, nine plates were prepared before one of 

 the necessary accuracy was obtained, and over 900 determinations of 

 the proportion of gold present in the assay pieces were made. It was 

 found that in general there was a tendency for the outside of the 

 ingots to be richer in gold than the interior, but that this distribution 

 was hardly so regular, and was not so pronounced as that observed in 

 a contrary sense, in standard silver, in which case silver accumulates 

 in the centre of the mass. 



It may be added that the differences in composition of different 

 parts of the gold bars, though small, are many times larger than the 

 possible errors of assay. 



The plates were of various dimensions, and were prepared from 

 pure gold and electrodeposited copper, well stirred to ensure uniformity 

 while in the molten condition, cast in iron moulds coated with carbon,, 

 and rolled out to a width of about 17 '5 cm., a thickness of 1 mm., 

 and a length of from 1 to 1'25 metres, the weight being from 3'7 to 

 .4*6 kilos. Series of discs were then cut out in parallel lines, one 

 down the centre of the plate, and two others distant 1 cm. from the 

 .edges. In the case of plate No. 1, intermediate series of discs were cut 

 half way between the centre line and the edges. The means of all 

 assays of each series taken from three typical plates were as follows,, 

 each result giving the mean of from 21 to 27 assays : 



In the case of standard silver plates of the same size prepared in a. 

 similar way, the difference between the amounts of silver in the richest 



* Eose, ' Chem. Soc. Journ.,' vol. 63 (1893), p. 704. 



