164 METALS AND THEIR COMBINATIONS. 



Analytical reactions. 



(A solution of aluminum sulphate, A1 2 (SO 4 ) 3 , or of aluminum chloride, 

 A1 2 C1 6 , may be used.) 



1. To solution of an aluminum salt add potassium or sodium 

 hydroxide : a white gelatinous precipitate of aluminum hydroxide, 

 A1 2 (OH) 6 , is produced, which is soluble in excess of the alkali. 



2. To aluminum solution add ammonium hydroxide : the same 

 precipitate as above is obtained, but it is insoluble in an excess of the 

 reagent. 



3. The carbonates of ammonium, sodium, or potassium produce 

 the same precipitate with liberation of carbon dioxide. (See expla- 

 nation above.) 



4. Ammonium sulphide produces the same precipitate with libera- 

 tion of hydrogen sulphide : 



A1 2 C1 6 + 3(NH 4 ) 2 S + 6H 2 = A1 2 (OH) 6 + 6NH 4 C1 + 3H 2 S. 



5. Sodium phosphate produces a precipitate of aluminum phos- 

 phate, soluble in acids. 



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 cerous oxalate, 

 Ce 2 (C 2 O 4 ) 3 9H 2 O, which is the only official cerium preparation. Cerium oxa- 

 late 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. 



QUESTIONS. 231. Mention some varieties of crystallized aluminum oxide 

 found in nature and some silicates containing it. 232. Give the general 

 formula of an alum, and mention some alums. 233. Which alum is official, 

 how is it made, what are its properties, and what is it used for? 234. What 

 is dried alum, and how does it differ from common alum ? 235. How is alu- 

 minum chloride made, and how is the metal obtained from it? 236. State the 

 properties of aluminum. 237. What change takes place when ammonium 

 hydroxide, and what change when sodium carbonate is added to a solution of 

 alum ? 238. What is the composition of earthenware, porcelain, and glass ; 

 how and from what materials are they manufactured ? 239. What is ultra- 

 marine? 240. Give tests for aluminum compounds. 



