xvi WATER AND THE ELEMENTS COMPOSING IT 239 



We have hence completely proved our previous ideas to be 

 correct, for we had been led to believe that water contained 

 hydrogen and oxygen. We have found it is an oxide of hydrogen. 

 Hence we may now say : Hydrogen in burning produces water 

 which is, therefore, an oxide of hydrogen. 



We should next examine the flask itself Avhich we used for the 

 preparation of the hydrogen in order to see whether any other 

 products have been formed, and to find out what has become of 

 the zinc. 



EXPT. 246. Filter off the liquid in the flask from the un- 

 dissolved zinc (sufficient zinc should be used to leave a quantity 

 still uiidissolved ; if all has disappeared add more and wait till 

 the action ceases). Partially evaporate the liquid and allow it 

 to crystallise. You will find that a quantity of clear colour- 

 less crystals are formed. Examine them and sketch the most 

 perfect. Heat some of the crystals in a tube and observe that 

 they melt, give off water (which can be collected and proved 

 to be water), and leave a white powder. 



These crystals are a compound formed from the zinc and part 

 of the sulphuric acid, and are known as zinc sulphate. Many 

 crystals behave similarly on heating, i.e., lose water 

 which they previously contained, and become con- 

 verted to a powder. The water contained in a 

 crystal and evolved on heating is known as water 

 of crystallisation. We may therefore state sul- 

 phuric acid and zinc form hydrogen and zinc 

 sulphate. 



Proportions of Oxygen and Hydrogen in 

 Water. We must next endeavour to find the 

 proportions in which the oxygen and hydrogen com- 

 bine during the formation of water. We may do 

 this in either of two ways, viz., by finding the 

 weight of the gases or by finding the volume of 

 the gases which combine. For the latter it is 

 necessary to measure out definite volumes of oxygen 

 and hydrogen, cause them to combine, then measure 

 the volume of gas which remains uncombined and 

 ascertain which gas it is. This is usually done in 

 a piece of apparatus known as an Eudiometer 

 (Fig 124.). In its simplest form this consists of a 

 long glass tube closed at one end and graduated in Eudiometer. 





