METALLURGY. 



1. ASSAYING PROCESS ; AXALYTLCAI, 



1. Old cupellation furnace, supposed to have been the 

 one used by Sir Isaac Newton, when Master of the 

 Mint, in some experiments on the cupellation of silver. 



18*76. Lent by the Master of tie Mint. 



In general construction it is precisely similar to those nowiii 

 use, the only difference; being that, in modern forms, more perfect 

 means are adopted for regulating the draught. 



2. Touchstone for the assay of gold, formerly used in 

 the Royal Mint. 



1876. Lent by the Master of lite Mint. 



The method is based on the fact that the greater the amount 

 of gold contained in an alloy, the brighter is the gold yellow 

 colour of a streak drawn with it on a black ground, and the less 

 is it attacked by pure nitric acid or by a " test " acid. In ascer- 

 taining the richness of the alloy under examination its streak 

 is compared with marks drawn with alloys whose richness is 

 accurately known. 



3. Muffle furnace used by gold and silver assay ers. 

 Presented by the Morgan Crucible Company, Limited, 

 E. 96. 1885. Eattersea. 



k Gold melting furnace. (French pattern.) 

 Presented by the Morgan Crucible Company, Limited, 

 E. 97. 1885. Battersea. 



5. Case showing successive processes of gold assaying. 



1876. Lent by the Master of the Mint. 



The process of gold assaying comprises six distinct operations. 



1st Process. The portion. of metal to be assayed is adjusted to 

 an exact weight by cutting and filing (we specimen A. in Case). 

 Such accurately weighed portions of alloy are wrapped, together 

 with definite weights of pure silver (B), in capsules of lead foil 

 (C C 1 ), and placed in order on a tray. 



2nd Process. The packets are transferred to porous cups or 

 " cupels" of phosphate of lime (bone ash), which are arranged in 

 rows, corresponding to those on the tray, in the muffle, or small 

 oven, No. 8, which is fixed in a suitable furnace and maintained 

 at a bright red heat. The lead oxidises and is absorbed hy the 



