134 MANUFACTURE OF FERTILIZING MATERIALS 



little more of the fine copper oxide is then used 

 to rinse off the watch-glass, the whole amount 

 being just about sufficient to fill the tube loosely 

 without shaking down to the depth of about 

 4 in. 



Coarse granular copper oxide, about 8 in. 



Metallic copper, preferably in the form of 

 a closely rolled coil of fine wire gauze, 3 in. 



Coarse granular copper oxide about 2 in. 



Asbestos plug. 



Lay the tube so charged in the trough of a 

 combustion furnace and fit tightly into the open 

 end a rubber stopper carrying a glass tube con- 

 nected by means of a rubber tube with another 

 tube dipping into the mercury in the azotometer. 



The end carrying the rubber stopper should 

 project from the furnace far enough to avoid 

 charring the rubber. 



Then heat up the magnesium carbonate, 

 starting cautiously at first so as not to break the 

 tube. The air in the tube is thus driven in to 

 the azotometer. When the bubbles of gas rising 

 through the mercury are completely absorbed 

 by the caustic alkali in the upper part of the 

 azotometer, heat up the copper oxide at the other 

 end of the tube, using the same caution as before, 

 carrying the heat slowly back until the metallic 

 copper as well as a couple of inches of the cop- 

 per oxide on each side of it is at a full red heat. 

 Lower the heat on the magnesium carbonate, 

 pinch the rubber connection between the com- 



