IRON, ALUMINUM, ETC. 145 



water. Filter if the solution is not clear, and divide the filtrate 

 into two portions. To the first portion, add a few drops of ammo- 

 nium hydroxid until a precipitate is obtained. To the second portion, 

 add about 5 drops of strong nitric acid. Heat to boiling ; when 

 cool, add ammonia to neutralize the acid and precipitate the iron. 

 The nitric acid oxidizes the iron and changes it from the ferrous 

 to the ferric condition. Compare the two precipitates. 



Questions. ( I ) What was formed when NH 4 OH was added to 

 FeSO 4 ? Write the reaction. (2) Give the color and other physical 

 properties. (3) What change did the HNO 3 produce ? (4) What 

 change did you observe in the color of the solution during the 

 boiling? (5) What was produced when NH 4 OH was added to 

 Fe(OH) 3 ? Write the reaction. (6) Give the color and some of 

 the physical properties. (7) How does this last precipitate differ 

 from the first one obtained ? 



Experiment j/. Dissolve i gram tannic acid in 25 cc. of hot 

 water. Dip a piece of cotton cloth into this solution. Dry the 

 cloth and then dip it into a solution of ferrous sulfate (i gram per 

 25 cc. of water). After the cloth has dried, see if the color can be 

 removed by washing. Add 5 cc. of ferrous sulfate solution to 5 cc. 

 of tannic acid solution. Observe the result. The FeSO 4 forms, 

 with the tannic acid, iron tannate. 



Questions, (i) Would the FeSO 4 alone give the same color 

 to the cloth? W T hy? (2) Was the color produced a permanent 

 one? (3) Tea contains tannic acid ; why does tea prepared in an 

 iron kettle give a black infusion ? (4) What was produced when 

 the solution of FeSO 4 was added to the tannic acid ? 



184. Occurrence of Aluminum. Aluminum is a gray- 

 ish white metal much lighter than iron and of greater 

 tensile strength and is found mainly as one of the constitu- 

 ents of clay that is formed from the disintegration of 

 feldspar, a double silicate of potassium and aluminum. 

 It is also found in other combinations, as in mica and 

 cryolite, and is present in nearly all soils and in small 



