400 ELEMENTARY CHEMICAL MICROSCOPY 



chlorides are obtained with the chlorides of Al, Cr, Ba, Sr, Ca, 

 K, Na, Li. 1 



The cesium chloride test is made more satisfactory and much 

 more sensitive by obtaining an iodo-salt instead of that described 

 above. This is accomplished by adding a fragment of potassium 

 iodide to the test drop after applying the cesium chloride. Crys- 

 tals of a double iodide of cesium and antimony having the same 

 form as the double chloride are obtained but they are deep orange 

 yellow or orange red instead of colorless. The composition of 

 these crystals is not well established, but the weight of evidence 

 seems to be that three molecules of Csl unite with two or three 

 molecules of Sbl 3 , rather than with SbL.. 



The test thus performed is an excellent one, but requires con- 

 siderable experience in order to properly control the conditions. 

 The test drop must be neither dilute nor concentrated and only 

 just sufficient hydrochloric acid should be present to prevent an 

 antimonyl compound from forming. It is also better to adopt 

 for this iodide modification the method of applying the reagents 

 suggested by Schoorl, 2 namely adding a fragment of cesium 

 chloride to one side of the drop and a fragment of potassium 

 iodide to the opposite side. 



The double iodide of bismuth separates in rhombs and elon- 

 gated hexagons, rarely in the regularly formed hexagons of the 

 antimony salt. Their color is a deeper orange (or even a red) 

 than that of the antimony double iodide. 



Tin forms yellow cesium iodostannate in regular octahedra. 



Precautions. 



When iodine separates it is an indication that too small an 

 amount of potassium iodide is present. 



In the event of a precipitate resulting upon the addition of 

 hydrochloric acid at the beginning (Ag, Pb, Hg, Cu) sufficient 

 acid should be added to complete the reaction. Decantation or 

 filtration should then be resorted to and the clear solution care- 

 fully concentrated to remove the excess of acid until a drop of 



1 Vermande: Pharm. Weekblad, 65 (1918), 1131. 



2 Beitrage z. mikrochem. Anal. Wiesbaden 1909, p. 49. 



