Rhombic tin

The Aiiotropes of Tin Tin Pest. Metallic tin may occur in three allotropic forms (see Textbox 19) the common form of tin, also known as white tin or beta tin, is stable at ambient temperatures its stability extends between -18°C and 170°C below -18°C tin is converted to a gray powdery allotrope, known as alpha tin or tin pest. A third allotrope, known as rhombic tin, is the form of tin stable at temperatures above 170°C. If ordinary white tin remains for extended periods of time at temperatures below -18°C, therefore, it is slowly converted to the gray, brittle, and powdery allotrope tin pest the conversion is accelerated at still lower temperatures. Tin objects kept in regions of the world where extremely low temperatures (below -18°C) prevail, initially... 

Tin exists in three different forms (allotropes). Grey tin has a diamond structure, a density of 5.75 gem-3 and is stable below 286 K. White tin exists as tetragonal crystals, has a density of 7.31 gem-3 and is stable between 286 and 434 K. Between 434 K and the melting point of tin, 505 K, tin has a rhombic structure, hence the name rhombic tin , and a density of 6.56gem-3. 

Metallic tin has many allotropic forms rhombic white tin (also called /3-tin) is stable at temperatures above 13 °C, whereas the stable form at lower temperatures is cubic grey tin (also called a-tin). A transition such as tin(white) tin ey) is called a solid-state phase transition. 

Working first with Polanyi, Weissenberg, and Brill, and later as the leader of the Textile Chemistry Section, Mark successively published papers on the crystal structures of hexamethylenetetramine, pentaerythritol, zinc salts, tin, urea, tin salts, triphenylmethane, bismuth, graphite, sulfur, oxalic acid, acetaldehyde, ammonia, ethane, diborane, carbon dioxide, and some aluminum silicates. Each paper showed his and the laboratory s increasing sophistication in the technique of X-ray diffraction. Their work over the period broadened to include contributions to the theories of atomic and molecular structure and X-ray scattering theory. A number of his papers were particularly notable including his work with Polanyi on the structure of white tin ( 3, 4 ), E. Wigner on the structure of rhombic sulfur (5), and E. Pohland on the low temperature crystal structure of ammonia and carbon dioxide (6, 7). The Mark-Szilard effect, a classical component of X-ray physics, was a result of his collaboration with Leo Szilard (8). And his work with E. A. Hauser (9, 10, 11) on rubber and J. R. 

It forms silver-white, rhombic crystals,7 of density 7-83, and melting point 1020° C. according to Hilpert and Dieckmann8 or 1031° C. according to Friedrich.9 It is non-magnetic. Steel-grey crystals of the arsenide of density 7-94 have been found associated with tin sulphide in the hearth of an old tin smelting furnace in Cornwall.10... 

Pyromelane. Rammelsbergite (See Moresonite) NiAs, Tin-white 6-9 5-5-6 Rhombic... 

Tin trimethyl suiphate crystallises in brilliant rhombic pyramids, for which a b c =0-8872 1 l-OSSS. ... 

Tin tri-o-tolyl chloride crystallises from alcohol in thick, colourless prisms, M.pt. 99 5° C. The bromide forms compact, rhombic plates, M.pt. 99-5° G., and the iodide rhombic crystals, M.pt, 119 5° C. The solubilities of these three compounds are similar to the corresponding para compounds. 

Tin tri-p-tolyl chloride forms rhombic j)lates, M.pt. 97 5° C, from hot alcohol. It is easily soluble in benzene or ether, sparingly in absolute alcohol The bromide crystallises in colourless rhomboids, M.pt. 98-5° C., and has a similar solubility to the chloride. The iodide crystallises in a like form to the bromide and melts at 120 5° C, and has also a solubility similar to the chloride. The fluoride forms hair-fine needles, melting in a sealed tube at 305° C. to a brown liquid. It is readily soluble in alcohol, but insoluble in ether. 

Tin ethyl phenyl dichloride, Sn C2H5)(C6H5)Cl2, is prepared by the action of stannic chloride on tin triethyl phenyl. It forms rhombic plates, M.pt. 45° C., easily soluble in ammonia and alcohol, but with difficulty in water or dilute hydrochloric acid. 

Besides grey tin and white tin, the crystalline form of which is tetragonal, there exists a third or rhombic form which is stable above 202 8°. The brittleness which is developed in tin when heated above about 200° is due to the change from the tetragonal to the rhombic form. 

No doubt bismuth was known at a much earlier date, but its history is confused because it was called marcasite, a name that has been used for many other substances also and is now mainly used to denote a rhombic variety of iron pyrites FeS2. Most of the later writers regarded it as a semi-metal. Barba, a South American priest, wrote in 1640 that bismuth had been discovered in Bohemia and that it was a metal somewhat like a cross between tin and lead, without being either of the two . It was apparently used in the manufacture of pewter rendering it harder and more sonorous. Hellot, the French chemist noticed that Cornish smelters added it to their metal, and in 1737 he succeeded in preparing a button of bismuth from a cobalt ore. Geoffroy in 1753 showed conclusively that bismuth was not a variety of lead, but a distinct metallic species. 

---