184 Miscellaneous Intelligence. 



introduced, suspended upon golden wires. After a few minutes, a 

 copper wire is to be immersed, and left until the gold has acquired 

 a deep colour ; it is then to be withdrawn, but the articles still left 

 in until they have acquired the colour necessary. They are then 

 to be put into warm water, acidulated by sulphuric or acetic acid, 

 to remove particles of oxide of copper, washed in clean warm water, 

 and dried near a fire. 



Generally, a single operation is not enough ; for, as a long im- 

 mersion produces harm from the oxide of copper, it is better to 

 shorten it, and repeat the operation. The colour produced by 

 several immersions is always the best ; that by one long immersion 

 is red, and often requires the article to be entirely cleaned and 

 recoloured. 



The mixtures above have been used for golden articles containing 

 one fourth of copper ; other alloys would probably require other 

 proportions. When the articles are large and thick, the immersion 

 should be longer than for small, thin, or narrow ones. As the bath 

 is good in proportion to the gold it contains, when, by successive 

 colorations, that has been removed, a few drops of muriate of gold 

 should be added, and sometimes portions of the other constituents 

 and of water. The copper wire is oxidized in the process, and 

 sometimes covered with a film of gold, in which case it should be 

 changed or cleaned. If an intense yellow colour is required, the 

 immersion should be frequently repeated, and the copper brought 

 into contact. If a pale colour is required, the last immersion 

 should be at the boiling point, and the copper wire ought not to 

 touch. 



Bronze articles, gilt by amalgamation, may be coloured in the 

 same way ; but M. Castellani has not as yet determined the best 

 mixture for the bath. — Bull. Univ., E. xii. 23. 



23. Berzelius's Analysis of Platina Ores — Native Platina of 

 Nischne Tagilsk in the Oural. — This ore is of a dull grey colour, 

 and contains many magnetic grains, some of which are polar. 

 These were analyzed apart from the rest, and gave a difference in 

 composition nearly constant. • 



i 



Platina i , 



Iridium • 



Rhodium . • 



Palladium • . 



Iron • 



Copper . , 



Osmiuret of iridium # 



Insoluble • » 



98.75 97.86 



* Mixture of osmiuret of iridium in grains and scales with sand. 



