ALUMINUM. 291 



4. Solution of ammonium sulphide produces the same precipitate, 

 with generation of hydrogen sulphide : 



A1 2 (S0 4 ) 3 + 3(NH 4 ) 2 S + 6H 2 = 2A1(OH), + 3(NH 4 ) 2 SO 4 + 3H 2 S. 



5. Solution of sodium phosphate produces a white precipitate of 

 aluminum phosphate, A1PO 4 .4H 2 O, soluble in mineral acids, but not 

 acetic, and in fixed alkalies (difference from iron). 



6. Heat a dry aluminum salt on charcoal strongly with the blow- 

 pipe flame. The residue is aluminum oxide, which, when moistened 

 with solution of cobalt nitrate and again heated, gives a blue com- 

 pound, cobalt aluminate. 



Test 1 combined with Tests 5 and 6 are conclusive. evidence of the 

 presence of aluminum. The salts are white, have a sweetish, astringent 

 taste, are acid to litmus, and decomposed by heat, leaving a residue 

 of oxide. 



Cerium, Ce = 141. This element occurs in nature sparingly in a few rare 

 minerals, chiefly as silicate in cerite. In its general deportment cerium resem- 

 bles aluminum. Cerous solutions give with either ammonium sulphide or 

 ammonium and sodium hydroxide, a white precipitate of cerous hydroxide, 

 Ce 2 (OH) 6 . Ammonium oxalate forms a white precipitate of cerium oxalate, 

 ceriioxalas, Ce 2 (C 2 4 ) 3 10H 2 O, which is the only official cerium preparation. 

 Cerium oxalate is a white, granular powder, insoluble in water and alcohol, 

 but soluble in hydrochloric acid. Exposed to a red heat it is decomposed and 

 converted into reddish-yellow eerie oxide. If this oxide, or the residue obtained 

 by heating any cerium salt to red heat, is dissolved in concentrated sulphuric 

 acid, and a crystal of strychnine added, a deep blue color appears, which 

 changes first to purple and then to red. The official cerium oxalate contains 

 also a small quantity of the oxalates of didymiuin, lanthanum, and other rare 

 earths. 



Monazite sand, found in North Carolina and elsewhere, contains, besides 

 cerite. the silicates or oxides or phosphates of other earth metals, especially 

 of zirconium, erbium, and thorium. It is chiefly the oxide of thorium which is 

 used in the mantle of the Welsbach incandescent burner, on account of the 

 bright white light which this oxide emits at a comparatively low temperature. 



QUESTIONS. Mention some varieties of crystallized aluminum oxide found 

 in nature and some silicates containing it. Give the general formula of an 

 alum, and mention some alums. Which alum is official, how is it made, what 

 are its properties, and what is it used for? What is dried alum, and how does 

 it differ from common alum? How is aluminum chloride made, and how ia 

 the metal obtained from it? State the properties of aluminum. What change 

 takes place when ammonium hydroxide, and what change when sodium car- 

 bonate is added to a solution of alum ? What is the composition of earthen- 

 ware, porcelain, and glass ; how and from what materials are they manufac- 

 tured? What is ultramarine ? Give tests for aluminum compounds. 



