OSMIUM. — IRIDIUM.— RHODIUM, 121 



except gold and platinum. It is not used for any 

 purpose. 



When heated in an open vessel it is oxidized, 

 and there are two oxides of tungsten. The pro- 

 toxide is of a brown colour, and when heated it 

 burns, and is converted into the peroxide^ which is 

 yellow, and has some of the properties of an acid, 

 being capable of combining with salifiable bases. 



The mineral called wolfram is composed of 

 tungstic acid, manganese, iron, and tin. 



OSMIUM. 



This metal was discovered by Mr. Tennant, in 

 the ore of platina. The metal is of a dark grey 

 colour, and is oxidized when heated. Its oxide is 

 volatile, and has a peculiar smell. It is little known, 

 and has not been fused. 



IRIDIUM. 



This metal was also discovered by Mr. Tennant, 

 in the ore of platina. It is of a wliitish colour. 

 It is fusible, and malleable. It unites with oxygen, 

 and alloys with the metals. Its combinations are 

 little known. 



RHODIUM. 



Dr. WoUaston discovered this metal in the ore 

 of platina. It is very infusible, and forms malleable 

 alloys with the malleable metals. It unites to 

 oxygen like all the other metals, but is very little 

 known. 



