_Procedure._—Use a metal or a glass flask connected with a condenser so
that the distillate may drop from the condenser tube directly into a
Nessler tube or a flask. Free the apparatus from ammonia by boiling
distilled water in it until the distillate shows no trace of ammonia.
After this has been done empty the distilling flask and measure into it
500 cc. of the sample, or a smaller portion diluted to 500 cc. with
ammonia-free water. If the sample is acid or if the presence of urea is
suspected add about 0.5 gram of sodium carbonate before distillation.
Omit this if possible as it tends to increase “bumping.” Apply heat so
that the distillation may proceed at the rate of not more than 10 cc.
nor less than 6 cc. per minute. Collect the distillate in four Nessler
tubes, 50 cc. to each tube, or if the nitrogen is high in a 200 cc.
graduated flask. These receptacles contain the ammonia nitrogen to be
measured as hereafter described.
Use Nessler tubes of such diameter that the graduation mark is between
20 and 25 cm. above the bottom and of such uniformity of diameter that
the distance from the bottom to the graduation mark of the longest tube
shall not exceed that of the shortest tube by more than 6 mm. The tubes
must be of clear white glass with polished bottoms.