§ 85. DETERMINATION OP NITROGEN. 119 



a. First clean and dry the tube thoroughly, and seal up 

 the point of the beak ; then put in the throat, where the 

 beak widens out into the tube, a loose plug of freshly ig- 

 nited asbestus ; rinse the tube out with a little soda-lime, 

 about half fill it with the same reagent, freshly ignited 

 and still warm, empty this soda-lime into a warm, dry 

 mortar, and mix intimately with it, by gentle trituration, 

 without much pressure, a carefully weighed quantity of 

 from 0.2 to 0.5 grm. of the finely powdered and well- dried 

 substance ; the quantity to be taken depends upon the 

 richness of the substance in nitrogen ; fill about 3 cm. of 

 the tube with soda-lime, and transfer this mixture into it 

 from the mortar, by scooping it up carefully with the 

 open end of the tube, over a sheet of dark-colored glazed 

 paper ; carefully rinse the mortar and pestle into the tube 

 with several small portions of the soda-lime, and finally, 

 when the tube is filled to within about 4 cm. of the end, 

 close it with another plug of freshly ignited asbestus, and 

 rap it gently on the table several times, in order to se- 

 cure an open space in the upper part of it for the passage 

 of gases. 



h. In some cases, as in the analysis of Peruvian guano 

 for example, the evolution of ammonia is liable to begin 

 as soon as the substance and soda-lime are brought to- 

 gether. If there is danger of this, fill about 10 cm. of 

 the tube with soda-lime, which should be but very slightly 

 warm, if at all, then put in the substance, fill 10 cm. more 

 with the reagent, and mix the two together as rapidly as 

 possible by means of a wire, bent in the form of a cork- 

 screw at the end ; if this is moved backwards and for- 

 wards, and twisted round a few times, through the sub- 

 stance and the soda-lime, a very perfect mixture can bo 

 quickly made ; before taking the wire out, put in about 

 10 cm. more of soda-lime, and work the corkscrew back 

 and forth through this to clean it, and then fiinish filling 

 the tube as in a. 



