xvi WATER AND THE ELEMENTS COMPOSING IT 247 



7. If twenty volumes of hydrogen and twenty-five volumes of 

 oxygen be mixed in an eudiometer and exploded, what volume of gas 

 would be left, and how would you show which gas it was ? 



8. What is the action of hydrogen on heated copper oxide ? How 

 can this action be used to find the composition of water by weight ? 



9. What tests would you apply in order to determine whether a 

 given colourless, odourless, tasteless liquid was water or not? 



10. What is meant by "hard" and " soft" water? How would 

 you determine which of two samples of water was the harder ? 



11. In what respects do natural waters differ from pure water, and 

 how are the differences brought about ? 



12. How could you prove that some w r ater is produced during the 

 combustion of coal gas ? 



13. What is an eudiometer ? Give a sketch of one and explain 

 for what purposes it may be used. 



14. How would you prove that when hydrogen is passed over 

 heated copper oxide something is taken away from the latter 

 compound ? 



15. _ You are required to prove experimentally that in the previous 

 question the part abstracted is really oxygen. How* would you 

 endeavour to do so ? 



16. Describe the apparatus you would use for the production and 

 collection of hydrogen gas ; name the materials required and 

 describe the properties of the gas. 



17. Write down what you consider to be the physical and 

 chemical characteristics of water, that is, the properties which are 

 possessed by water, but by no other substance. 



18. Describe a method of liberating hydrogen from water (a) at 

 a red heat ; (b) at ordinary temperatures. 



