34O AGRICULTURAL, ANALYSIS 



present, is used for the determination. Into the closed end of 

 the combustion tube put a small loose plug of asbestos, and upon 

 it to the depth of about four centimeters, fine soda-lime. In a 

 porcelain dish or mortar mix the substance to be analyzed, thor- 

 oughly but quickly, with enough fine soda-lime to fill approxi- 

 mately 1 6 centimeters of the tube, or about 40 times as much soda- 

 lime as substance, and put the mixture into the combustion tube 

 a quickly as possible by means of a wide-necked funnel, rinsing 

 out the dish and funnel with a little more fine soda-lime, which 

 is to be put in on top of the mixture. Fill the rest of the tube to 

 within about five centimeters of the end with granulated soda- 

 lime, making it as compact as possible by tapping the tube gently 

 while held in a nearly upright position during the filling. The 

 layer of granulated soda-lime should not be less than 12 centi- 

 meters deep. Lastly, put in a plug of asbestos about two centi- 

 meters long, pressed rather tightly, and wipe out the end of the 

 tube to free it from adhering particles. 



Connect the tube by means of a well-fitting rubber stopper or 

 cork with the U-tube or Will's bulbs, containing 10 cubic centi- 

 meters of standard acid, and adjust it in the combustion furnace 

 so that the end of the tube projects about four centimeters from 

 the furnace suitably supporting the U-tube or Will's bulb. Heat 

 the portion of the tube containing the granulated soda-lime to a 

 moderate redness, and when this is attained extend the heat grad- 

 ually through the portion containing the substance, so as to keep 

 up a moderate and regular flow of gases through the bulbs, main- 

 taining the heat of the first part until the whole tube is heated 

 uniformly to the same degree. Continue the combustion until 

 gases have ceased bubbling through the acid in the bulbs, and 

 the mixture of substance and soda-lime has become white, or 

 nearly so, which shows that the combustion is finished. The 

 combustion should occupy about three-quarters of an hour, or not 

 more than one hour. Extinguish the burners and when the tube 

 has cooled below redness break off the closed tip and aspirate air 

 slowly through the apparatus for two or three minutes to bring 

 all the ammonia into the acid. Disconnect the tube, wash the 

 acid into a beaker or flask, and titrate with the standard alkali. 



