ANALYSIS OF COMPLEX MATTER 139 



The flame is now removed, and the tube and contents cooled, 

 while the air is still excluded. Copper will now be seen in 

 the place of the copper oxide. It is again slightly warmed, 

 and at once placed in the desiccator to cool, and afterwards 

 weighed. We have now all the data which are needed for 

 determining the quantity of copper in a known quantity of 

 copper oxide. 



It is evident that we are assuming in this experiment 



TO GAS 



Fig. 47. 



both the purity of the copper oxide and the identity of the 

 red substance with copper. 



92. Copper Oxide is caused to yield up its Oxygen when 

 it is raised in Temperature and a Stream of Hydrogen is 

 passed over it. The Hydrogen and Oxygen under these Con- 

 ditions combine chemically and form Water, The Water 

 is Collected and Weighed. In the previous experiment 

 attention was only directed to the quantity of copper con- 

 tained in a given quantity of copper oxide. In the following 



