10 METHODS OF ANALYSIS [Chap. 



tube containing the metallic copper, the anterior layer of cupric oxid and the sodium 

 bicarbonate. As soon as the vacuum is destroyed and he apparatus filled w th 

 carbon dioxid, shut off the flow of mercury 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 escaping bubbles will pass into the air and not into the tube, 

 to avoid 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 

 minutes, to drive out anj^ moisture that may be present, and then bring to a red heat. 

 Heat gradually the mixture of substance and oxid, lighting a 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 burners 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 bubbles has ceased, turn out all the burners except those 

 under the metallic copper and anterior layer of oxid, and allow to cool for a few min- 

 utes. Exhaust with the pump and remove the azotometer before the flow of mercury 

 has stopped. Break the connection of the tube with the pump, stop the flow of 

 mercury, and extinguish the burners. Allow the azotometer to stand for at least 

 an hour, or cool with a stream of water until the volume and temperature become 

 constant. 



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

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

 barometer; calculate the weight of the nitrogen as usual. 



AMMONIACAL NITROGEN. 



32 Magnesium Oxid Method. — Official. 



Place 0.7-3.5 grams, according to the ammonia content, of the substance to be 

 analj'zed in a distillation flask with about 200 cc. of water and 5 grams or more of 

 magnesium oxid, free from carbonates. Then connect the flask with a condenser and 

 distil 100 cc. of the liquid into a measured quantity of standard acid and titrate 

 with standard alkali solution. 



NITRIC AND AMMONIACAL NITROGEN. 



33 Ulsch-Slreet Method.— Official. 



Place 1 gram of the sample in a half-liter flask, add about 30 cc. of water and 2-3 

 grams of reduced iron, and, after standing sufficiently long to insure solution of the 

 soluble nitrates and ammonium salts, add 10 cc. of a mixture of strong sulphuric acid 

 with an equal volume of water; shake thoroughl}', place a long-stemmed funnel in the 

 neck of the flask to prevent mechanical loss, and allow to stand for a short time until 

 the violence of the reaction has moderated. Heat the solution slowly, boil for 5 

 minutes, and cool. Add about 100 cc. of water, a little paraffin, and 7-10 grams of 

 magnesium oxid, free or nearly free from carbonates. Connect with a condenser, 

 such as is used in the Kjeldahl method, and boil the mixture for 40 minutes, nearly 

 to dryness; collect the ammonia in a measured quantity of standard acid, and titrate 

 with standard alkali solution in the usual manner. The nitrogen obtained represents 

 the nitrates plus the ammonium salts contained in the sample. 



In the analysis of nitrate salts proceed as above, except that 25 cc. of the nitrate 

 solution, equivalent to 0.25 gram of the sample, are emplo3^ed with 5 grams of re- 

 duced iron. After boiling add 75 cc. of water and an excess of sodium hydroxid 

 solution and complete the determination as above. 



