422 ELEMENTARY CHEMICAL MICROSCOPY 



ARSENITES. 



a. With Silver Nitrate. See Arsenic, page 397. 



BORATES. 



a. With Ammonium Fluoride in Dilute Hydrochloric Acid Solu- 

 tion. Add to the drop on a celluloid slip NaCl, or BaCl2, then 

 the reagent, then a trace of HC1. See Sodium, page 325. 



Precautions. Silicon, titanium and zirconium must be absent. 

 The test drop must be moderately concentrated. 



b. Test with a Turmeric Viscose Silk Fiber. See page 309. 



BROMIDES. 



a. Staining Starch Yellow. 



To a drop of the solution to be tested add a trace of dilute 

 sulphuric acid, warm very gently. Cool. Add a very little potato 

 starch, just enough to give a few granules in the center of the 

 drop. Introduce at the center of the drop a small crystal of 

 ammonium persulphate. Bromine is set free and colors the 

 starch granules yellow. If iodides are present the starch will 

 be colored blue or violet. 



Too long and too high heating will result in the loss of hydro- 

 bromic acid. 



If too much sulphuric acid or too much persulphate is added 

 the starch granules will be destroyed. 



The preparation must be cool when the starch is added, other- 

 wise the granules will be destroyed. 



The preparation must be examined at once, otherwise the 

 yellow color will have disappeared. 



b. Silver bromide (and silver chloride) is soluble in ammonium 

 hydroxide; silver iodide is not. 



CARBONATES. 



a. Characterized by Effervescence with hydrochloric or sul- 

 phuric acid. Gas bubbles visible in gelatin. See page 311. 

 Cyanates give a similar reaction, carbon dioxide being formed by 

 the reaction between cyanate and acid. 



b. In Solutions of Carbonates, Lead Acetate produces charac- 

 teristic crystals of lead carbonate, in the form of acicular 



