March 15, 1935
ANALYTICAL EDITION
81
with standard thiosulfate. Table I11 shows the effect of varying conditions, 1.0 gram of potassium bromide having been used throughout. Teorell (11) has introduced a sensitive micromethod for ammonia, back-titrating the excess hypobromite with naphthyl red. It seems probable that calcium hypochlorite could profitably be substituted in this method as well, being more stable than the sodium hypobromite originally specified.
titration of the excess arsenite with standard hypochlorite solution) yielded excellent results and is especially advantageous in the presence of colored compounds or in the determination of extremely small amounts of ammonia with reagents 0.01 I\i or even more dilute. The data in Table V show that quantities of ammonia as small as 0.5 mg. in a volume of 25 cc. can be determined with a maximum error of about 2 per cent, using the general procedure described above. The iodometric procedure yields TABLE IV. DETERMINATION OF AMMONIA IN ALKALINE MEDIUM errors of the same magnitude hpt is preferable in the absence NITROQEN TIMEOF NITROGEN SALTS of other oxidizing substances, since the color change of the TAkEX BUFFER STANDING FOUNDERROR PRESENT iodine starch is sharper than that of Bordeaux in these very Grams M i n . 1MQ. Me. MQ. % dilute solutions. Blanks should be run along with the de10.51 5 NaHCOt 3 10.61 11.0 ... 10.51 10.55 3 NaHCOa 3 +0.4 ... terminations, as traces of reducing substances are likely to be 10.51 10.61 1 NaHCOs 3 0.0 ... 10.51 10.52 1 NaHCOs 12 +o. 1 present in the water used as a solyent and some bromine or ... 14.06 15 14.01 0.5 NaHCOs 4-0.4 oxygen may be lost by decomposition of the hypobromite on 5 +0.2 14.04 14.01. 0.5 NaHCOs 14.05 14.01 0.5 NaHCOa 5 f0.3 30
