MERCURY, SILVER, GOLD, AND* PLATINUM. 271 



this respect, for no heat can decompose the latter. The 

 compound, then, of gold with chlorine can be called an un- 

 stable compound, as are its compounds with oxygen. 



Chloride of gold is used to a limited extent in the arts, 

 chiefly in photography. 



384. Platinum. The color of this metal is between tin 

 and steel. It is the heaviest of all substances ; it has great 

 ductility and tenacity ; it is very malleable, especially when 

 heated, and it may then be welded, though not as perfectly 

 as iron. In fusibility this metal stands at one end of the 

 scale of metals, mercury being at the other. Mercury may 

 be said to melt at about 40 below zero ; while, on the other 

 hand, platinum withstands the heat of the hottest furnace, 

 and requires the intense heat of the oxyhydrogen blowpipe 

 to melt it. Hence the crucibles of the chemist are often 

 made of this metal. It is used, also, somewhat in the arts 

 in the manufacture of apparatus for the distillation of 

 sulphuric acid, and in enameling glass and porcelain. If it 

 were an abundant metal, it might be put to many common 

 uses, and be a great convenience, for the utensils made of 

 it would never rust, and would not be in any danger of 

 melting, and when they became dirty they could be cleaned 

 and made bright again by heating them red-hot. 



Platinum, like gold, dissolves in aqua regia only ; the so- 

 lution on evaporation gives a deliquescent brown-red mass 

 consisting of platinic chloride, PtCl 4 . This is used in chem- 

 ical laboratories as a test solution, and in photography to a 

 limited extent. 



385. " Dobereiner's Lamp." By a certain chemical process 

 platinum may be obtained in a finely divided state, furnish- 

 ing a soot-like substance called " spongy platinum." This 

 produces remarkable effects upon certain gases. If a little 

 of it be introduced into a mixture of oxygen and hydrogen 

 gases, an explosion is produced as quickly as if a lighted 



