LESSONS IN CHEMISTRY. 161 



After oxygen and silicon the most abundant element is the 

 metal ALUMINIUM (Al). It is a tin- white, malleable, ductile, 

 sonorous metal. It is lighter than most other metals and yet 

 it is very strong, approaching iron in this respect. It is never 

 found pure in nature, but is an abundant ingredient in many 

 minerals. The double silicate of aluminium and potassium 

 AlKSi 3 8 a constituent of feldspar, is abundant in trap rock, 

 basalt, mica, and porphyry. Aluminium silicate is the chief 

 ingredient of clay, shale and slate. Aluminium oxide, A1 2 3 , 

 called alumina is nearly pure in the ruby, sapphire and emery. 

 This metal is an ingredient of several double sulphates called 

 alums, as AlK(SO- 4 ) 2 +12H 2 potassium alum, AlNa(S0 4 ) 2 4- 

 12H 2 sodium alum, A1NH 4 (S0 4 ) 2 -|-12H 2 ammonium alum. 



Aluminium hydrate (A10 3 H 3 ) combines readily with many or- 

 ganic coloring matters, forming insoluble compounds. To a so- 

 lution of common alum add a solution of cochineal, and to the 

 mixture add a little ammonia when a colored precipitate of alu- 

 minium hydrate and cochineal will be formed, which is called 

 carmine lake. Similar precipitates may be formed with other or- 

 ganic coloring matters. Fiber of cotton that has been soaked in 

 a solution of alum will retain colors which the cotton alone can- 

 not hold. Soak a piece of cotton cloth in alum water and let it 

 dry a day or two, then treat it and a piece of ordinary cotton 

 with a solution of logwood an*d observe the difference in the 

 amount and permanence of the color taken by the two pieces. 

 Substances having this property are called mordants. 



Clay, aluminium silicate, is the material of which all grades of 

 porcelain and pottery ware and all kinds of brick, tile and terra 

 cotta are made. Clay mixed with water may be moulded in any 

 required shape and after drying may be burned so as to become 

 firm and durable, but pure clay shrinks so much in burning that 

 articles made of it lose their shape and often crack, so that in 

 making bricks, pottery, etc., more or less sand is added to the 

 clay making a mixture which shrinks less and holds its form 

 better than pure clay. 



Bricks are made of a great variety of material and vary in 

 I., s.-u 



