298 Domestic Science 



calculated and should approximately be 8. As the 

 mean result of the best determinations, the value 

 7-94 is now generally accepted. The student must 

 not expect to obtain a very close approximation to 

 this value at the first attempt, but a fair degree of 

 accuracy may be attained by careful attention to the 

 directions supplied. 



Hydrogen + copper oxide = copper + hydrogen oxide. 



Exercise for Student. 



Having given that the specific gravity of hydrogen is 0*00008989, 

 and that of oxygen 0'0011054, find what volume of hydrogen will 

 combine with 1 c.c. of oxygen. 



204. It is interesting to note that the oxide of iron 

 produced in Experiment 130 may be once more reduced 

 to the metallic state if a hydrogen generator be substi- 

 tuted for the flask and the jar be replaced by a flask 

 floating on cold water, the end of the delivery tube 

 being inserted into the mouth of the flask. Pass a 

 steady stream of hydrogen from the generator through 

 the tube containing the iron oxide for three minutes. 

 Next heat the tube to dull redness, allowing the gas 

 to pass continuously. In a short time small drops of 

 water will fall into the flask, and, by sufficiently 

 prolonging the experiment, the whole of the oxygen 

 may be removed from the oxide in this way. 

 Hydrogen + triferric tetroxide = iron + hydrogen oxide. 



On examining this equation, it will be seen that it 

 is the reverse of that given at the end of Experiment 130. 

 Many other cases are known of similar reactions, 

 which may take place in opposite ways according to 

 the conditions of the experiment. In that just de- 

 scribed the steam produced is carried away by that part 

 of the stream of hydrogen which is unaffected and thus 



