mixture, add hydrochloric acid, a drop at a time, until the solution just clears (R). Now pass hydrogen sulfide through the clear solution until an orange-colored solid forms (R).

d. Boil a small amount of powdered antimony with concentrated nitric acid (hood) until it is changed into a white powder. Dilute the mixture with water, filter, and wash the residue on the filter paper with water. Convince yourself that the residue is not a nitrate. It is a hydrated oxide of variable formula, but may be considered to have the formula Sb,O,. Dissolve a portion of it in sodium hydroxide (R). Dissolve another portion in hydrochloric acid (R).

150. Bismuth. a. Repeat § 146, a, substituting bismuth for arsenic. Contrast the action of heat on arsenic, on antimony, and on bismuth.

b. Repeat § 149, c, substituting bismuth for antimony and using nitric acid alone as the solvent.

CHAPTER XXV

BORON AND SILICON

151. Borax bead. a. Make a little loop on the end of a platinum wire and heat it to redness in a Bunsen flame; then quickly bring the loop in contact with some borax and reheat. The borax adhering to the loop will swell up (why?) and finally form a clear glass bead. Now dip the bead into a solution of a cobalt compound and reheat thoroughly (R).

b. Repeat the experiment, substituting a compound of chromium for the cobalt solution.

152. Boric acid. a. Dissolve 5 g. of borax in 15 cc. of boiling water. Test the solution with litmus paper. Explain. Add to the hot solution 5 cc. of concentrated hydrochloric acid. Cool the solution, filter off the precipitate (R). Compare the precipitate with borax as to solubility in alcohol.

b. Place 1 cc. of a solution of borax in an evaporating-dish and add a few drops of sulfuric acid (R) and 2 or 3 cc. of alcohol. Set fire to the alcohol and watch for a green color in the flame. This is a test for boric acid. Will borax act in the same way if no sulfuric acid is added?

c. Heat a little boric acid in an iron crucible until a clear liquid is formed (R).

153. Borax. Prepare a concentrated solution of borax and add a few drops of a solution of silver nitrate. The precipitate is silver borate (R). Add a few drops of the concentrated solution of borax to a test tube half full of water, and then test with silver nitrate. The precipitate is silver oxide (R). Compare it with the precipitate formed by the action of very dilute sodium hydroxide on silver nitrate (R). How do you account for the different actions of borax on silver nitrate ?

154. Silica. a. Mix about half a gram of fine sand with 3 or 4 times its weight of solid sodium hydroxide. Place the mixture in an iron dish, and heat until fusion has taken place and the fused mass has again become solid (R). Then dissolve the product in hot water.

b. Pour half of the solution into a test tube and add an excess of hydrochloric acid. Allow it to become perfectly cold. What is the jellylike substance?

c. Transfer the remainder of the solution to an evaporatingdish, acidify with hydrochloric acid (R), evaporate to dryness, and heat the dish gently with the bare flame (R). Is the product soluble in water? in acids? in alkalis? in fused sodium hydroxide?