Keychain. Praseodymium.

<div>   </div> <div> <strong> Atomic number       <span class = "Apple-tab-span" style = "white-space: pre;"> </span>59</strong></div> <div> <strong> Atomic mass       <span class = "Apple-tab-span" style = "white-space: pre;"> </span> 140,91</strong></div> <div> <strong> Density, kg / m ? <span class = "Apple-tab-span" style = "white-space: pre;"> </span>     6780 </strong> </div> <div> <strong> Temperature </strong></div> <div> <strong> melting, ° С         935 </strong> </div> <div>   </div> <div> Praseodymium is a moderately soft, malleable, ductile silver-white metal. Praseodymium was discovered in 1885 by the Austrian chemist Karl Auer von Welsbach. He established that the element didyme, discovered in 1839 by the Swedish chemist Karl Mosander, is a mixture of two elements with similar physical and chemical properties, which he named neodymium and praseodymium. Praseodymium is obtained in a mixture with other rare earth elements. Praseodymium ions are used to excite laser radiation with a wavelength of 1.05 μm (infrared radiation). Praseodymium fluoride is used as a laser material. Praseodymium oxide is used to melt glass, to which its addition imparts a pale green color. </div> <div>   </div> <div>   </div>