98 



GENERAL SCIENCE 



Experiment 28. Bring a bottle of pure hydrogen over a 

 lighted candle. Notice that the gas takes fire at the mouth of 



. . the bottle and burns quietly, 



while the flame on the candle is 

 extinguished as the bottle is 

 further lowered. Remove the 

 bottle slowly and the -candle will 

 be relighted as the wick passes 

 through the burning hydrogen 

 (Figure 94). 



The most important prop- 

 erty of hydrogen is its com- 

 bustibility. The flame is 

 exceedingly hot, but not very 

 luminous. When it burns in 



FIG. 94. Hydrogen burns but does pure oxygen, it is the hottest 



not support combustion. 11/1 



ot all names, burning at a 



temperature of nearly 4000 C. It is much used in the 

 melting of certain metals and the cutting of steel. A six- 

 inch shaft of solid steel has been cut in less than forty 

 seconds with such a flame (Figure 95). 



Three States of Water. Water occurs quite commonly 

 in all three states of matter solid, liquid, and gaseous. 

 The liquid form is most common and the name " water " 

 is usually applied to this state; however, when water 

 is vaporized or when it freezes and becomes a solid, it 

 does not cease to be water. The water that is contained 

 in the air is sometimes called " water vapor " or steam, 

 while the solid form is called ice. 



Freezing of Water. - - The temperature at which water 

 freezes is definite and under ordinary circumstances is 

 always the same. On the Centigrade thermometer the 

 freezing point of water is taken as the starting point in 

 making the scale and is called zero. On the Fahrenheit 



