220 METALS AND THEIR COMBINATIONS. 



3. Many other reagents cause the separation of metallic gold from 

 its solution, as, for instance, oxalic acid, sulphurous and arsenous 

 acids, potassium nitrite, etc. 



Platinum, Pt = 194.3. Platinum, like gold, is found in nature in 

 the free state, the chief supply being derived from the Ural moun- 

 tains, where it is found associated with a number of metals (iridium, 

 ruthenium, osmium, palladium, rhodium) resembling platinum in 

 their properties. 



Platinum is of great importance and value on account of its high 

 fusing-point and its resistance to the action of most chemical agents, 

 for which reason it is used in the manufacture of vessels serving in 

 chemical operations. 



Platinum, when dissolved in nitro-hydrochloric acid, forms platinic 

 chloride, PtCl 4 , a salt frequently used as a reagent for potassium or 

 ammonium salts, with which it forms insoluble double chlorides of 

 the composition PtCl 4 .(KCl) 2 and PtCl 4 .(NH 4 Cl) 2 . By heating the 

 latter salt sufficiently it is decomposed and metallic platinum is left 

 as a gray spongy mass. 



Molybdenum, Mo = 95.9. This metal is found in nature chiefly 

 as sulphide, MoS 2 , from which, by roasting, molybdic oxide, MoO 3 , 

 is obtained. The oxide, when dissolved in water, forms an acid 

 which combines with metals, forming a series of salts termed 

 molybdates. Of interest is ammonium molybdate, a solution of which 

 in nitric acid is an excellent reagent for phosphoric acid, with which 

 it forms a yellow precipitate, insoluble in acids, soluble in ammonium 

 hydroxide. 



QUESTIONS. 301. How is antimony found in nature, and what are the prop- 

 erties of this metal ? 302. State the composition of antimonous sulphide, and 

 its color when crystallized and amorphous. 303. How do hydrochloric acid 

 and alkali hydroxides act upon antimonous sulphide ? 304. What is the sul- 

 phurated antimony of the U. S. P. ? 305. Mention the two chlorides of anti- 

 mony and state their properties. 306. How is antimonous oxide made, and 

 what is it used for? 307. Give tests for antimony. 308. State the use made 

 of tin in the metallic state ; mention the two chlorides of tin, and what stannous 

 chloride is used for. 309. How are gold and platinum found in nature ; by 

 what acid may they be dissolved, and what is the composition of the com- 

 pounds formed ? 310. Which is the most important compound of molybdenum, 

 and what is it used for ? 



