348 ELEMENTARY CHEMICAL MICROSCOPY 



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 C^Snle of less solubility than the chloro- 

 stannate. The iodo-compound separates in yellow cubes and 

 octahedra. 1 



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 M 2 RCl6, M 2 RBr 6 

 and M 2 RI 6 , M may be K, Rb, Cs, (NH*) and R may be Se, Te, 

 Sb, Pb, Sn, Pt, Ir, Os, Pd, Ru. All salts of this series are iso- 

 morphous (Groth). 



EXPERIMENTS. 



Defer until Bi is being studied. 



ARSENIC. 



Crystal Forms and Optical Properties of Common Salts of 



Arsenic. 



A . ISOTROPIC. Trioxide (I, also, but rarely mono- 

 clinic) . 

 B. ANISOTROPIC. 



Hexagonal. Triiodide; silver arsenate (second- 

 ary, normal is I ?). 



Tetragonal. Secondary potassium arsenate. 

 Orthorhombic. Calcium -ammonium arsenate; 

 magnesium-ammonium arsenate. 



1 It is probable that the product actually obtained is a solid solution of Cs 2 SnI 6 

 in CsoSnCk 



