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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

THULIUM (Thule, the earliest name for Scandinavia), Tm; at. wt. 168.934; at. no.69; m.p. 15450C; b.p. 17270C; sp. gr. 9.314 (25a); valence 2, 3. Discovered in 1879 by Cleve. Thulium occurs in small quantities along with other rare earths in a number of minerals. It is obtained com- mercially from monazite, which contains about 0.007 % of the element. Thulium is the least abundant of the rare-earth elements, but with new sources recently discovered, it is now considered to be about as rare as silver, gold, or cad- mium. Ioncxchange and solvent extraction techniques have recently permitted much easierseparation of the rare earths, with much lower costs. Thulium metal, only a few years ago, was not obtainable at any cost; in 1950 the oxide sold for $450/gm. Thulium metal now costs from $3 to $20/grit depending on the purity, quantity, and supplier. Thulium can be isolated by reduction of the oxide with lanthanum metal or by calcium reduction of the anhydrous fluoride. The pure metal has a bright, silvery luster, It is reasonably stable in air, but the metal should be protected from moisture in a closed container. The element is hard, silver-gray, soft, malleable and ductile, and can be cut with a knife. Sixteen isotopes are known,- with atomic masses ranging from 161 to 176. Natural thulium, Tm169, is stable. Because of the relatively high price of the metal, thulium has not yet found many practical applications. Tm16-9 bombarded in a nuclear reactor can be used as a radiation source in portable x-ray equipment. Tm171 is potentially useful as an energy source. Natural thulium also has possible use in ferrites (ceramic magnetic materials) used in microwave equipment. Thulium metal (99.9%) costs about $3/gm. or $1200/lb. As with other lanthanides, thulium has a low to moderate acute toxic rating. It should be handled with care. TIN (Anglo-Saxon, tin), Sh (L. stannum); at. wt. -118.69; at. no.50; m.p. 231.89; b.p. 22700C; sp. gr. (gray) 5.75, (white) 7.31; valence, 2, 4. Known to the ancients. Tin is found chiefly in cassiterite (5n02). Most of the world's supply comes from Malaya, Bolivia, Indonesia, the Republic of the Congo, Thailand, and Nigeria. The U.S. produces almost none, although occurrences have been found in Alaska and California. Tin is obtained by reducing the ore with coal in a reverberatory furnace. Ordinary tin is com- posed of nine stable isotopes. Thirteen unstable isotopes are I I THE ELEMENT~Contiiiued) also known. Ordinary tin is a silvery white metal, is mal- leable, somewhat ductile, and has a highly crystalline struc- ture. Due to the breaking of these crystals, a "tin cry" is heard when a bar is bent. The element has two or perhaps three allotropic forms. On warming, gray or a tin, with a cubic structure, changes at 1 3.20C into white or fi tin, the ordinary form of the metal. White tin has a tetragonal structure. Some authorities believe a y form exists between 161 0C and the melting point; however other authorities discount its existence. When tin is cooled below 1 3.20C, it changes slowly from white to gray. This change is affected by impurities, such as aluminum and zinc, and can be prevented by small additions of antimony or bismuth. This change from the a to fi form is called "the tin pest". There are few if any uses for gray tin. Tin takes a high polish and is used to coat other metals to prevent corrosion or other chemical action. Such tin plate over steel is used in the so- called tin can for preserving food. Alloys of tin are very important. Soft solder, type metal, fusible metal, pewter, bronze, bell metal, Babbitt metal,. White metal, die casting alloy, and phosphor bronze are some of the important alloys using tin. Tin resists distilled, sea, and soft tap water, but is attacked by strong acids, alkalis, and acid salts. Oxygen in solution accelerates the attack. When heated in air, tin forms SnO2, which is feebly acid, forining stannate salts with basic oxides. The most important salt is the chloride (SnCl2 H20), which is used as a reducing agent and as a mordant in calico printing. Tin salts sprayed onto glass are used to produce electrically conductive coatings on the glass. These have been used for panel lighting and for frost- free windshields. Of recent interest is a crystalline tin- niobium alloy that is superconductive at very low tem- peratures. This promises to be important in the construction of superconductive magnets that generate enormous field strengths, but use practically no power. Such magnets, made of tin-niobium wire, weigh but a few pounds and produce magnetic fields, when started with a small battery, that are comparable to that of a 100-ton electromagnet operated continuously with a large power supply. The small amount of tin used in canned foods is quite harmless. The agreed limit of tin content in U.S. foods is 300 mg. per kg. The trialkyl and triaryl tin compounds, are used as biocides and must be handled carefully. Tin prices have varidd from Sot to about $2.00/lb. over the past 25 yrs. It presently costs about 51.90/lb.

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