xvi WATER AND THE ELEMENTS COMPOSING IT 243 



previously weighed. To the end attach a U-tube containing 

 calcium chloride, a substance which, we have already seen, 

 readily absorbs moisture. At A attach a tube, as shown, by 

 means of which dry hydrogen, as in Expt. 244, may be passed 

 through the tube AC. The U-tube of calcium chloride must 

 be carefully weighed before the experiment. When the hydro- 

 gen is passing, heat the tube AC, and observe that the black 

 colour of the copper oxide changes to the red colour of metallic 

 copper, and that water collects in the U"tube D. Take care 

 that no condensed water remains in AC ; if any is present, 

 heat it and drive it over into D. Allow the tube to cool, dis- 

 connect, and weigh the boat of oxide and the U-tube again. 

 Enter your results thus : 



Wt. of U-tube after experiment 3G '473 grains 



Wt. of U-tube before experiment 35 '821 grams 



Wt. of water produced '652 grams 



Wt. of boat of copper oxide before experiment ... 5*562 grams 

 Wt. of boat of copper oxide after experiment . . . 4*982 grams 



Wt. of oxygen 0' 580 grams 



The weight of oxygen is 0'580 gram, and that of the water 

 produced from it is 0'652 gram ; therefore the weight of 

 hydrogen must be 0'652-0'580 gram, that is, 0'072 gram. 

 Write, therefore : 



Wt. of water 0'682 gram 



Wt. of oxygen 0'580 gram 



Wt. of hydrogen ... '072 gram 



Therefore '072 gram hydrogen combines with "580 gram of oxy- 



F\Qn 

 gen, and hence 1 gram hydrogen combines with-- = 8 grams of 



oxygen. 



If the experiment is carefully performed this is the result 

 always obtained, so that we have found that Water is formed of 

 eight-ninths its weight of oxygen with one-ninth its weight 

 of hydrogen. 



K 2 



