MERCURY, SILVER, GOLD, AND PLATINUM. 273 



Take a common alcohol lamp, and, cutting the wick rather 

 short, surround it with a coil of small platinum wire about 

 half an inch high. Light the lamp, and when the wire be- 

 comes red-hot blow it out. The wire, in- 

 stead of cooling at once, as any common 

 wire would, will continue to glow till all 

 the alcohol is consumed. These curious 

 phenomena depend upon the power pos- 

 sessed by platinum of condensing gases 

 upon its surface. 



387. Iridium and Osmium. There are sev- 

 eral very rare metals found associated with platinum, 



and having similar properties. Two of these, iridium and osmium, form 

 the hardest alloy known, a mineral called by the mineralogist iridosmine, a 

 name compounded of the names of the two metals. One use has been 

 found for this mineral : it is used to point gold pens, its great hardness 

 fitting it admirably for that purpose. 



QUESTIONS. 



374. Whence the name mercury ? How can the evaporation of mercury 

 be shown? What is cinnabar? How is mercury obtained from it? 375. 

 What is vermilion ? When is it black ? W^hen red ? 376. What is the com- 

 position of calomel ? What of corrosive sublimate ? What are their prop- 

 erties ? What antidote is recommended ? How does it act ? 377. What 

 is amalgamation ? How carried on ? 378. What is said of the properties 

 of silver ? Its uses ? Explain the tarnishing of silver. 379. In what min- 

 eral does silver occur ? How is it extracted ? What is cupellation ? 380. 

 What is the composition and nature of lunar caustic, so called? 381. De- 

 scribe the silver assay. 382. How is gold found in nature ? With what is 

 it alloyed ? What are its properties ? Explain the term carat. 383. How 

 is gold chloride made? For what used? 384. Give in full what is said of 

 the properties and uses of platinum. In what acids does it dissolve ? 

 385. Describe and explain Dobereiner's Lamp. 386. Describe the experi- 

 ment with ether and a coil of platinum wire. Explain this briefly. 387. 

 What other metals belong to the platinum group ? 



M 2 



