126 ANSWEE8 TO PRACTICAL QUESTIONS 



22. Show that the earths crust is mainly composed of 

 burnt metals. 



(See Cooke's Religion and Chemistry?) 



It consists largely of potassium, magnesium, calcium, 

 aluminum, sodium, etc., in combination with O. These 

 compounds are the products of combustion. 



The elements O, Si, Al, Mg, Ca, K, Na, Fe, C, S, H, 

 Cl and N 13 in all probably make up 1 9 ^ r of the earth's 

 crust. 



23. What kind of iron is used for a magnet? For a 

 magnetic needle ? 



Steel. 



24. Why does a tin pail so quickly rust out when once the 

 tin is worn through ? 



The iron rusts rapidly in the presence of water, which 

 favors oxidation. 



25. Why is the zinc oxide found in New Jersey red, when 

 zinc rust is white ? 



The oxide in New Jersey is colored by compounds of 

 iron and manganese. 



26. Should we filter a solution of permanganate of potash 

 through paper ? 



(See Chemistry ', page 155, note.) 



No. The salt will give up O and corrode the filter. 



27. Why is wood, cordage, etc., sometimes soaked in a 

 solution of corrosive sublimate ? 



This salt possesses strong antiseptic properties. 



