HYDROGEN 157 



A small amount of the black oxide of copper is placed in the hard glass tube 

 AC, which is about 1-5 centimetres in diameter, and fitted with the tube D 

 in the manner shown. When you are sure that pure dry hydrogen is 

 escaping from the open end of D, heat the oxide of copper in the tube by 

 means of the burner E. In a few minutes moisture will be seen to collect 

 in the tube D, and presently to drop into the dish put to collect it. 



Examine the residue in the hard glass tube, and note its change to a 

 reddish colour ; this is due to the presence of copper. 



Rearrange the apparatus, using the U-tube G in the place of the tube D. 

 The U-tube G containing lumps of calcium chloride is employed to collect 

 the water formed. 



ii. Composition of water. Put some copper oxide into the tube AC, and 

 carefully weigh the tube. Similarly the weight of the U-tube G and its 

 contents must also be determined. As in the last experiment, when you are 

 sure pure dry hyxlrogen is escaping from the open end of G, heat the copper 

 oxide by means of the laboratory burner. Be sure that all the water formed 

 is collected by the U-tube. If any condenses at the end of the hard glass 

 tube AC, drive it over by heating the tube at this place. 



Allow the tube AC to^cool. Disconnect it at A and C, and again deter- 

 mine its weight and that of its contents. Notice the diminution in weight. 

 Also weigh the U-tube again, and observe its increases in weight. 



Relative weights of the constituents of water. To find the 

 composition of water by weight that is. the weights of oxygen and 

 hydrogen which combine to form water it should be noticed that only 

 the weights of two out of the three substances concerned are required, 

 i.e. the weights of hydrogen and water (or of oxygen and water) are 

 known, the weight of the oxygen (or hydrogen) is readily calculated. 

 The experiment is done by finding the weights of the oxygen and water, 

 and for this it is best to use, not oxygen itself, but some oxide which 

 readily gives up its oxygen to the hydrogen, so that by weighing the 

 oxide before and after the experiment we can ascertain the weight of 

 oxygen which it has lost. The oxide used for this purpose is usually 

 oxide of copper, a black powder, which it has been seen is obtained 

 when air is passed over red-hot copper. Pure dry hydrogen is passed 

 over the heated oxide, and it combines with the oxygen of the oxide 

 to form water and leaves the copper behind. 



By weighing the water produced and subtracting from it the weight 

 of the oxygen used, the weight of the hydrogen can be found. If the 

 experiment is carefully performed it is found that water is formed of 

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



This experiment, also taken in conjunction with other experiments 

 upon the volumes of the gases, proves further that any volume of 

 oxygen is 16 times heavier than the same volume of hydrogen. 



