270 GENERAL SCIENCE 



liberating carbon dioxide, which is caught by the sticky 

 mass of dough and gives to the dough a porous structure. 



Baking powder contains soda and cream of tartar. 

 When the powder is put in moist dough, the cream of 

 tartar acts as an acid on the soda, and carbon dioxide is 

 formed. Acid phosphate baking powders contain acid 

 calcium phosphate instead of cream, of tartar. 



Carbonates. Other common and useful carbonates 

 besides sodium carbonate are calcium carbonate and 

 potassium carbonate. 



Limestone is found in large quantities in the earth. 

 When it is heated to a high temperature, it is decomposed 

 into lime and carbon dioxide. Lime is used in many ways 

 as the binding material in mortar and plaster. 



Potassium carbonate is a white powder similar to sodium 

 carbonate. Wood ashes were for many years the sole 

 source of it. This is the reason it is called " potash," 

 from which the name potassium was. derived. 



Potassium carbonate was once used in making soaps, 

 but later methods use the cheaper sodium carbonate. 



QUESTIONS 



1. What fuel is most used in your city? Why? 



2. Why is dry wood a better fuel than green wood? 



3. Why is hard pine a good fuel wood? 



4. The flashing point of a sample of kerosene is 150 Fahrenheit. 

 What will it be Centigrade? 



5. Why does the carbon dioxide in soda water come to the 

 surface when the water is drawn ? 



6. How can you prove that carbon dioxide will not support 

 combustion? 



7. Should the ventilator in a hot-air system of heating be 

 placed at the top or bottom of a room? Why? 



8. How are the flues in a cook stove arranged to provide for 

 heating the oven? 



