1923] 



KLOTZ — NITROGEN METABOLISM IN FUNGI 



327 



The small quantity of reducing substances, other than dextrose, 

 found in the peptone media could not be satisfactorily removed 

 by precipitation with sodium tungstate as described for milk in 

 Shaffer & Hartmann's ('20) paper. Lloyd's reagent, 1 as em- 

 ployed by Folin and Bergland ('22) (in the determination of sugars 

 in urine), would adsorb some but not all of these reducing sub- 

 stances. Accordingly, in the later determinations the small 

 quantity of copper reduced by the peptone was estimated by 

 running blank determinations on the "peptone minus" (No. 2) 

 medium, and subtracting this result from that given by the 

 "peptone plus" (No. 1) medium. 



The principle of the Folin ('05) aeration method was used in 

 obtaining the results for ammonia nitrogen (see Shaffer, '03). 

 To make the solution strongly alkaline to phenolphthalein 0.1 

 ml. of a saturated NaOH solution was used for each 5 ml. of 

 unknown. The strong alkali is preferable to NajCOs because it 

 assures the freeing of the NH 3 from the small amount of 

 MgNH4P0 4 .6H 2 that may form in the alkaline solution (see 

 page 347). Tubes were connected in series so that 7 aerations 

 could be made at the same time. Folin tubes with perforated 

 bulbs were used throughout the apparatus for aerating the 

 unknown and for delivery of the NH 8 into the receiving liquid. 

 By means of a filter pump the solutions were aerated for 18-24 

 hours at the rate of approximately 50 liters of air per hour. In 

 this, as well as in the determinations for total and nitrate N, 

 4 per cent boric acid was used to collect the NH 3 . As in the 

 Scales and Harrison ('20) method for total N the collected NH t 

 was titrated directly against standard H 2 SO«, brom-phenol-blue 

 being used as the indicator. This was compared with the usual 

 method of collection in a standardized acid and titration back 

 against standard alkali; the boric acid modification is absolutely 

 as accurate as the old method and dispenses with the necessity of 

 a standard alkali (see also Paul and Berry, '21, and Spears, '21). 



Total N, including nitrates, was estimated by the method of 

 Davisson and Parsons ('19). In this the nitrates are first re- 

 duced to NH 3 by means of Devarda's alloy in alkaline solution, 

 the NH 8 being caught in strong H 2 S0 4 (7 parts H 2 S0 4 to 1 part 



1 A hydrated aluminum silicate obtained from Eli Lilly & Co., Indianapolis, Ind. 



