106 



KI.KMKNTS OF CKNKKAL SCIKNVF, 



for instance, it will take very much longer to cook food 

 materials ; and if the temperature is too low, it may be quite 

 impossible to cook certain foods. This, of course, applies only 

 to those foods that are cooked by boiling. 



On the other hand, increased pressure raises the boiling 

 point very decidedly. In the steam boiler, where steam is not 

 allowed to escape until it has reached a high pressure, the 

 pressure of the steam has the same effect upon the boiling point 



FIG. 57. Boiling point upon a mountain 



Mount Rainier, Washington. The figures show boiling points (Fahrenheit scale) 

 at different elevations when the air pressure is 30 inches at sea level 



as does the increased pressure of the atmosphere. The boiling 

 point under additional pressure of 30 pounds to the square 

 inch is 120.6 C., at 100 pounds it is 155 C., and at 300 

 pounds it is 100 C. 



The boiling point is also raised by the presence of any solid 

 substance (salt, for instance) which is dissolved in water. 



119. Other facts about steam. When water changes into 

 steam, it increases enormously in volume if it is free to expand. 

 Steam at atmospheric pressure may occupy about 1600 times 



