402 ELEMENTARY CHEMICAL MICROSCOPY 



B. ANISOTROPIC. 



Hexagonal. — Sulphate (9 H 2 0). 



Tetragonal. — Bismuthyl chloride. 



Orthorhombic. 



Monoclinic. 



Triclinic. — Nitrate (?) ; bismuthyl nitrate. 



DETECTION. 



A. The Addition of Water to neutral or very faintly acid so- 

 lutions followed by the formation of a heavy white amorphous 

 or granular precipitate should lead to the suspicion of the 

 presence of bismuth. From the chloride, the compound BiOCl 

 is obtained and from the nitrate B1ONO3 • H 2 0. 



B. By Means of Potassium Sulphate. 



This test has been discussed at length under Sodium, 

 Method B. page 322, and also under Potassium, Method B, 

 page 330, to which the student is referred for details. 



Neither arsenic, antimony, nor tin yield a crystalline deposit. 

 The test is therefore one of the most satisfactory for the recog- 

 nition of bismuth, providing lead is absent. Lead yields a gran- 

 ular or amorphous (or rarely crystalline) precipitate with potas- 

 sium sulphate. It is therefore necessary to. first remove the 

 lead by precipitating with sulphuric acid in the presence of 

 nitric acid before proceeding to test for bismuth. With this 

 end in view add to the solution to be tested nitric acid, then a 

 drop of very dilute sulphuric acid — if no precipitate results, 

 evaporate until fumes of sulphur trioxide are formed. Then 

 proceed as described under Method 77, page 300, Experiment a 

 If a precipitate forms with the sulphuric acid decant, centrifuge 

 or filter the solution to remove the lead, after which evaporate 

 with sulphuric acid and proceed as above. 



C. By Means of Cesium Chloride. 



This test has already been discussed under Antimony, 

 Method A, page 398. 



The only specific difference between the double chlorides of 

 these two elements is that with bismuth there is a greater ten- 

 dency toward rhombic plates. Conversion into double iodides 

 gives a salt darker colored than that with antimony. 



