394 ELEMENTARY CHEMICAL MICROSCOPY 



appears as irregular or thin rectangular prisms with parallel 

 extinction and exhibits brilliant polarization colors. 



Iron, copper and antimony are apt to be adsorbed by the 

 tin oxide; in such an event yellow or red double chlorides of 

 copper or iron and cesium will eventually make their appearance. 

 Occasionally if much iron is present the crystals of cesium chloro- 

 stannate are colored yellow. 



Lead if present may give octahedra of cesium chloroplumbate, 

 Cs 2 PbClo. 



As already noted, antimony gives hexagons and bismuth rhombs 

 of the corresponding chloroantimonate and chlorobismuthate. 



In the event of no precipitate appearing after some time, add a 

 fragment of potassium iodide. This may lead to the formation 

 of cesium iodostannate, Cs2Snl6, of less solubility than the chloro- 

 stannate. The iodo-compound separates in yellow cubes and 

 octahedra. 1 Yellow or orange cesium dichloriodide may form. 



In testing for tin in alloys it is usually sufficient to dissolve 

 in nitric acid (i : i), evaporate to dryness, moisten with nitric 

 acid and again evaporate to dryness. Extract the white residue 

 with dilute nitric acid to remove interfering elements, dissolve 

 in concentrated hydrochloric acid, drive off excess of acid, dilute 

 and test. 



In order to obtain good crystals it is essential that the test 

 drop be dilute before the cesium chloride is added. 



In the case of simple salts or mixtures it is usually sufficient to 

 convert into chlorides by evaporating with hydrochloric acid; 

 then dissolve in water, acidulate with hydrochloric acid and add 

 the drop of cesium chloride solution. But in such an event one 

 must remember that double chlorides of Sb, Bi, Cu, Fe, Al, Zn, 

 Cd, Pb, etc., will almost invariably separate if present. 



If much tin is thought to be present use rubidium chloride in 

 preference to cesium chloride. 



Note. — It is of considerable theoretical interest to note that 

 in the compounds of the type just considered M2RCI6, MoRBr 6 

 and M 2 Rl6, M may be K, Rb, Cs, (NH4) and R may be Se, Te, 



1 It is probable that the product actually obtained is a solid solution of Cs-^Snl* 

 in Cs-iSnCU. 



