FERTILIZERS. 9 



(&) Azotometer of at least 100 cc capacity, accurately calibrated. 



(c) Sprengel mercury air pump. 



(d) Small paper scoop made from stiff writing paper. 



(3) DETERMINATION. 



Use from 1 to 2 grams of ordinary commercial fertilizers. In the case of 

 highly nitrogenized substances, the amount to be used must be regulated by the 

 amount of nitrogen estimated to be present. Fill the tube as follows: (1) 

 About 5 cm of coarse cupric oxid. (2) Place on the small paper scoop enough 

 of the fine cupric oxid to fill about 10 cm of the tube, after having been mixed 

 with the substance to be analyzed; pour on this the substance, rinsing the 

 watch glass with a little of the fine oxid, and mix thoroughly with a spatula; 

 pour into the tube, rinsing the scoop with a little fine oxid. (3) About 30 cm 

 of coarse cupric oxid. (4) About 7 cm of metallic copper. (5) About 6 cm 

 of coarse cupric oxid. (6) A small plug of asbestos. (7) From 0.8 to 1 

 gram of sodium bicarbonate. (8) A large loose plug of asbestos. Place the 

 tube in the furnace, leaving about 2.5 cm of it projecting; connect with the 

 pump by a rubber stopper smeared with glycerol, taking care to make the con- 

 nection perfectly tight. 



Exhaust the air from the tube by means of the pump. When a vacuum has 

 been obtained, allow the flow of mercury to continue ; light the gas under that 

 part of the tube containing the metallic copper, the anterior layer of cupric 

 oxid (see (5) above), and the sodium bicarbonate. As soon as the vacuum is 

 destroyed and the apparatus filled with carbon dioxid, shut off the flow of mer- 

 cury and at once introduce the delivery tube of the pump into the receiving arm 

 of the azotometer just below the surface of the mercury seal so that the escap- 

 ing bubbles will pass into the air and not into the tube, thus avoiding the useless 

 saturation of the caustic potash solution. 



When the flow of carbon dioxid has very nearly or completely ceased, pass 

 the delivery tube down into the receiving arm, so that the bubbles will escape 

 into the azotometer. Light the gas under the 30 cm layer of oxid, heat gently 

 for a few moments, to drive out any moisture that may be present, and bring to 

 a red heat. Heat gradually the mixture of substance and oxid, lighting one 

 jet at a time. Avoid a too rapid evolution of bubbles, which should be allowed 

 to escape at the rate of about one per second, or a little faster. 



When the jets under the mixture have all been turned on, light the gas under 

 the layer of oxid at the end of the tube. When the evolution of gas has 

 ceased, turn out all the lights except those under the metallic copper and ante- 

 rior layer of oxid, and allow to cool for a few moments. Exhaust with the 

 pump and remove the azotometer before the flow of mercury is stopped. Break 

 the connection of the tube with the pump, stop the flow of mercury, and extin- 

 guish the lights. Allow the azotometer to stand for at least an hour, or cool 

 with a stream of water until a permanent volume and temperature have been 

 reached. 



Adjust accurately the level of the potassium hydroxid solution in the bulb 

 to that in the azotometer; note the volume of gas, temperature, and height of 

 barometer ; make calculation as usual or read results from tables. 



(f) MAGNESIUM OXID METHOD. OFFICIAL. 

 (Applicable only to the determination of ammonia.) 



Place from 0.7 to 3.5 grams of the substance to be analyzed, according to the 

 proportion of ammonia present, in a distillation flask (p. 6, (2), (a) ), with about 



