MICROCHEMICAL REACTIONS OF THE COMMON ACIDS 375 



BORATES. 



a. With Ammonium Fluoride in Dilute Hydrochloric Acid Solu- 

 tion. Add to the drop on a celluloid slip NaCl, or BaCl 2 , then 

 the reagent, then a trace of HC1. See Sodium, page 279. 



Precautions. Silicon, titanium and zirconium must be ab- 

 sent. The test drop must be moderately concentrated. 



b. Test with a Turmeric Linen Fiber. See page 261. 



BROMIDES. 



a. Staining Starch Yellow. 



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

 sulphuric acid, warm 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. 



The preparation must be cool when the starch is added, 

 otherwise 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 sulphuric 

 acid. Gas bubbles visible in gelatin. See page 263. Cyanates 

 give a similar reaction, carbon dioxide being formed by the reac- 

 tion between cyanate and acid. 



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

 istic crystals of lead carbonate. 



c. To test the character of the gas given off, place in the distilling 

 apparatus, Fig. 130, page 245, exposing a drop of lead acetate 

 to the vapors. 



