602 EVERYDAY SCIENCE 



over a coal fire, but the waste is considerable if measured gas is 

 the fuel used. It has been estimated that certain kinds of scale 

 offer from twenty to fifty times the resistance to heat that is offered 

 by an equal thickness of wrought iron. 



If the tea-kettle is washed daily, or even three times a week, 

 and scoured if necessary with Bon Ami or Old Dutch Cleanser, 

 scale will not accumulate. 



Housekeepers who will not exercise this care, may put a piece of 

 limestone, rough marble, or oyster shell in the tea-kettle. Change 

 it for a fresh piece two or three times a month. 



PROJECT XXX. How to Remove Tea-kettle Scale, page 144 



Heavy Iron Kettles. To remove accumulated scale from a 

 heavy iron kettle, fill the kettle with cold water and add a heaping 

 tablespoonful of sal ammoniac. Bring this to a, boil and then 

 empty the kettle. Place the empty kettle over a flame until it is 

 very hot and the scale will peel off. Set the kettle aside and allow 

 it to cool slowly! Repeat if necessary. After the scale has been 

 removed and the kettle is cool, fill it with a strong solution of wash- 

 ing soda, boil, and rinse with clear hot water. 



Aluminum Kettles. In the case of an aluminum kettle, fill 

 with cold water, and add a heaping tablespoonful of oxalic acid 

 crystals. Boil the solution, let it stand all night, and boil again in 

 the morning. This will remove a thin scale, but the operation will 

 have to be repeated several times for a heavy scale. Afterwards 

 wash the kettle thoroughly with ordinary soap and warm water 

 and rinse with clear hot water to remove all trace of the poisonous 

 acid. 



Concentrated nitric acid will remove the scale from aluminum 

 much more quickly than oxalic acid, without injuring the aluminum. 

 But it has to be handled so carefully that it is not recommended 

 for ordinary household use. 



Strong alkalies dissolve aluminum. Never use them on that 

 metal for any purpose. 



Enamel Kettles. Scale does not tend to accumulate so rapidly 



