140 



ELEMENTS OF LABORATORY WORK 



experiment we trace the course of the oxygen leaving the 

 copper, and learn the relative quantities of oxygen and hydro- 

 gen which unite under these circumstances and form water. In 

 order to do this it is necessary to collect and weigh all the 

 water which is formed, and measure the loss of weight sus- 

 tained by the copper oxide. This is carried 011 in the following 

 experiment : 



A tube A of hard glass is partly filled with copper oxide, 

 and connected at one end with the supply of hydrogen B and 

 c, and at the other with the tube D which collects the water 

 formed. Before making the connection, the tube containing 

 the copper oxide is dried carefully and weighed, and the tube 

 D, which is filled with calcium chloride or phosphorus 



Fig. 48. 



pentoxide, is also weighed. The ends of the tube are tempo- 

 rarily closed, so that it does not abstract water vapour from 

 the air, during and after the operation of weighing. After 

 connecting together the parts of the apparatus, hydrogen is 

 prepared, by adding dilute hydrogen sulphate to the zinc con- 

 tained in the vessel c. The hydrogen leaving this vessel is 

 mixed with water vapour until it is dried by coming in con- 

 tact with calcium chloride or other drying substance placed 

 in the tube B. 



The copper oxide is now heated by a suitable flame, and 

 kept for some time at a low red heat. The temperature of 

 the tube is now allowed to fall, while hydrogen continues to 

 pass through it. It is weighed when cold. The loss of matter 

 is due to the oxygen, which has combined with some of the 



