21 

 PLATINOID METALS. 



The principal metals o£ the platinum group ^ve. platinum itself, Case 48, 

 iridium, and osmium, the two latter being frequently found 

 together forming the alloy osmiridium or iriJosmine. Practically 

 they are only found in alluvial deposits. 



Platinum fuses at exceedingl}^ high temperature only, and is 

 unattacked by most acids. It is, in consequence, largely used in 

 the form of wire, foil, and crucibles for chemical purposes.* 



Another important use of platinum is in the preparation of 

 the platinotype papers used in photography. 



Iridium and osmiridium are used in the manufacture of 

 incandescent mantles and, in the form of grains, for tipping 

 certain pens. A minute quantity is obtained from gold bullion 

 at the Eoyal Mint (5930). The grains are steely in colour and 

 generally flaky in nature. While platinum can be dissolved in 

 aqua regia (a mixture of one part of concentrated nitric acid 

 with four of hydrochloric), iridium and osmiridium are quite 

 insoluble. 9367 consists of iridium grains, and is believed to 

 have come from the Macleay River. 



Platinum has been found in certain deposits — rironstone and 

 the decomposed rocks beneath them — near Broken Hill. Assays Platimim. 

 give very varying results, but 2 oz. per ton have been obtained. 

 There is at present no prospect of successfully working the 

 material. Specimens are exhibited. 



Beach Sands. — On both the Australian and American coasts 

 of the Pacific, the beach sands are sometimes found to carry 

 gold and platinum. Por convenience, specimens of such sands 

 from New South Wales, although in reality worked for gold, are 

 placed here. It is on the Northern beaches only, and more 



* The hi^^h price of platinum articles has given rise to the wide-spread fallacy that crude 

 platinum is more valuable ihan gold, no allowance being made for the treatment that has. 

 to be underg-on'.- befor ■- it is converted into a commercial product. While gold is found in a 

 state of comparative purit.y, requiring fluxing only to free it from gangue, or alloyed with 

 silver from which it can be readily s ^parated, crude platinum, as will be seen by reference 

 to the analjsis given with 5369 (page 23), is alloyed with iron, osmium, iridium", and other 

 substances whicli have to be separated from it. Moreover, Mhile the value of fine gold 

 remains fixed at eighty-four shillings per ounce troy, th.it of platinum fluctuates, and can be 

 controlled to some extent by interested parties. 



