EXAMINATION OF COMMERCIAL FERTILIZERS 133 



tion is actually begun. The magnesium car- 

 bonate is again heated at the close of the opera- 

 tion to drive the nitrogen remaining in the tube 

 into the azotometer. 



The azotometer is a graduated tube, with 

 stop-cock above and two side tubes below, at 

 different heights. The lower part of the azo- 

 tometer as well as the lower side tube is filled 

 with mercury. The upper side tube and the re- 

 mainder of the azotometer is filled (when ready 

 for use) with a strong solution of caustic potash 

 (to absorb carbon dioxide). The upper side tube 

 is connected with a stop-cock bulb containing 

 the caustic alkali. The bulb is supported in 

 such a way that it can be raised and lowered 

 at will. 



The copper oxide should be ignited and 

 cooled before using. The portion which is to be 

 mixed with the substance must be ground in 

 a mortar until it is reduced to a fine sand. 



Select a tube of good hard glass which is 

 sealed at one end of a length of about 24 to 27 

 in. Charge as follows: 



Magnesium carbonate, crushed to pieces four 

 or five times the size of a pin's head, 1J to 2 in. 



Coarse granular copper oxide, 1| to 2 in. 



Fine copper oxide mixed with the substance, 

 4 in. 0.5 to 2 gms. of the fertilizer substance 

 are weighed out in a watch-glass, then mixed 

 with copper oxide, and poured into the tube by 

 the aid of a small paper scoop or funnel. A 



