Hemihydrate crystal characteristics

Properties Colorless to white crystals characteristic odor and taste. Mp (anhydrous form) 97C, mp (hemihydrate) 78C, bp 167C, sublimes easily. Soluble in alcohol and glycerol, hot water, ether, chloroform, and volatile oils. 

If soluble anhydrite is desired, firing is maintained until a second boil occurs accompanied by a second temperature plateau at about 190°C. Virtually all the water of crystallization has been removed at 215°C. Soluble salts are impurities that increase the vapor pressure within the kettle. Aridized stucco refers to ketde-calcined hemihydrate that has been made with the intentional addition of 0.55—1.1 kilograms of NaCl or CaCl per metric ton of land plaster. The stucco characteristic of lower water demand permits higher density and higher strength casts. The hygroscopic nature of the chlorides prevents the use of aridized stucco for some applications. 

Thiamine chloride hydrochloride (mol.wt. 337.28) forms colourless monoclinic crystals, m.p. 248-250° (under decomposition). Under certain conditions it also crystallizes with m.p. 232-234° (dimorphism). It has a characteristic odour and a slightly bitter taste. The chloride hydrochloride crystallizes from alcohol-water solutions as the hemihydrate, but on exposure to... 

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