MICROCHEMICAL REACTIONS OF TIN 393 



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TIN. 



Crystal Forms and Optical Properties of the Common 



Salts of Tin. 

 A. ISOTROPIC. Tetraiodide (I); potassium chloro- 



stannate (I). 



B. ANISOTROPIC. 



Hexagonal. 



Tetragonal. 



Orthorhombic . Tetrabromide. 



Monoclinic. Stannous chloride + 2 H 2 0; stan- 



nous fluoride, stannic chlorides. 

 Triclinic. 



DETECTION. 



A . By Means of Cesium Chloride. 



Apply reagent by Method /, page 299. 



In testing for tin it is best to evaporate to dryness repeatedly 

 with moderately concentrated nitric acid, thus converting the 

 element into the insoluble dioxide. The dry residue is extracted 

 repeatedly with dilute nitric acid to remove interfering elements 

 and finally dissolved in aqua regia and the excess of acid removed 

 by evaporation. Dissolve the moist residue in water. There 

 is thus obtained a compound which we may term chlorostannic 

 acid, 1 with which cesium salts yield an immediate precipitate 

 of cesium chlorostannate C^SnCle in the form of tiny colorless 

 highly refractive regular octahedra and cubes. Rubidium gives 

 a similar compound of greater solubility and therefore yielding 

 larger crystals, but of sufficiently high solubility to render the 

 separation of the crystalline phase too slow to be of practical 

 use. These three chlorostannates are isomorphous. The am- 

 monium salt is more soluble than the above and the presence of 

 ammonium compounds is therefore objectionable; the same is 

 true of sodium which yields Na2SnCle 5 H^O. The latter salt 



1 This compound may also be regarded as a hydrated stannic chloride. If evapo- 

 rated to dryness there will b'e obtained SnCU-xHoO, where x is 3, 5 or 8. All three 

 salts are crystalline and all can be referred to the monoclinic system. 



