EXAMINATION OF COMMERCIAL FERTILIZERS 135 



bustion tube and the azotometer for a moment, 

 open the upper stop-cock of the azotometer, 

 and by raising the bulb force the gas out of the 

 azotometer. Close the azometer stop-cock and 

 release the connection. Then carry the heat 

 slowly back to the mixture of the substance or 

 fertilizer with the copper oxide, getting all of 

 the tube except the magnesium carbonate end 

 finally up to full red heat. The progress of the 

 combustion may be judged by the rapidity with 

 which the bubbles of gas pass through the mer- 

 cury. It should not be faster than about two 

 bubbles per second. 



When they cease, heat up the magnesium 

 carbonate again, keeping up the heat until the 

 gas driven from the tube is all absorbed by the 

 caustic alkali. Then disconnect the azotometer, 

 and cool down the tube. Allow the azotometer 

 to stand for some time to cool completely, and 

 hang it near a thermometer. Bring the bulb 

 close to the azotometer, and raise or lower it 

 until the level of the solution in both is the same. 

 Then read the volume of the gas and the tem- 

 perature, and calculate the weight of the nitrogen. 



When not in use the azotometer should be 

 washed free from caustic alkali, especially as to 

 the stop-cock, which should always be taken 

 out, wiped off, and freshly lubricated with a 

 little vaseline. 



Potassium. Weigh out 10 gms. of fertilizer 

 material, Dissolve in a porcelain evaporating 



