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H' at. wt. (natural) 1.007967
   at. wt. (H') 1.007822
   at. no. 1
   m.p. - 259.140C
   b.p. - 252.870C 
   density 0.08988 gm./l
   density (liquid) 70.8 gm/i. (-2530C)
   density (solid) 7016 gm/i. (-2620C)
   valence 1.

**Electronic configuration**
K	L	M	N	O	P	Q
1	2	3	4	5	6	7
s	s p	s p d	s p d f	s p d f	s p d f	s p d f
1

PLATINUM (Sp. platina, silver), Pt; at. wt. 195.09; at. no.78; m.p. 17720C; b.p. 38271 1000C; sp. gr. 21.45 (200C); valence 1?, 2, 3, or 4. Discovered in South America by Ulba in 1735 and by Wood in 1741. The metal was used by pre- Colombian Indians. Platinum occurs native, accompanied by small quantifies of iridium, osmium, palladium, ruthen- ium, and rhodium, all belonging to the same group of metals. These are found in the alluvial deposits of the Ural moun- tains, of Colombia, and of certain western American states. Sperrylite (PtAs2) occurring with the nickel-bearing deposits of Sudbury, Ontario, is the source of a considerable amount of the metal. The large production of nickel offsets the fact that there is only one part of the platinum metals in two million parts of ore. Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda4ime- silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis. It is insoluble in hydrochloric and nitric acid, but dissolves when they are mixed as aqua regia, form- ing chloroplatinic acid (H2PtCI~),.an important compound. The metal is extensively used in jewelry, in wire and vessels for laboratory use, and in many valuable instruments, in- cluding thermocouple elements. It is also used for electrical contacts, corrosion-resistant apparatus, and in dentistry. Platinum~obalt alloys have magnetic properties. One such alloy made of 76.7% Pt and 23.3% Co, by weight, is an extremely powerful magnet that offers a B-H (max) almost twice that of Alnivo V. Platinum resistance wires are used for constructing high-temperature electric furnaces. The metal is used for coating missile nose cones, jet engine fuel nozzles, etc., which must perform reliably for long periods of time at high temperatures. The metal, like palladium, absorbs large volumes of hydrogen, retaining it at ordinary temperatures but giving it up at red heat. In the finely divided state platinum is an excellent catalyst, having long been used in the contact process for producing sulfuric acid. It is also used as a catalyst in cracking petroleum products. Fine platinum wire will glow red hot when placed in the vapor~of methyl alcohol. It acts here as a catalyst, converting the alcohol to formaldehyde. This phenomenon has been used commercially to produce cigarette lighters and hand warm- ers. Hydrogen and oxygen explode in the presence of platinum. The price of platinum has varied widely; more than a century ago it was used to adulterate gold. It was nearly eight times as valuable as gold in 1920; the present price is about 31 40/troy ounce.

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