Jan. 27. 1919 Influence of Salts on Nitric Nitrogen in Soil 109 



nitrogen -fixing powers of the soil were above the average, and previous 

 work had shown it to have an intensely interesting bacterial flora. 



Several hundred pounds of the soil were thoroughly mixed, stored in 

 a large box, and kept as near field conditions as possible so that all the 

 work could be done on the same soil. As the soil was needed in the 

 work, portions were brought to the laboratory, air-dried in the dark, 

 then weighed in loo-gm. portions into sterile covered tumblers. To 

 each of these were added 2 gm. of dried blood. The whole was then 

 carefully mixed, and the salt in most cases added from a carefully stand- 

 ardized stock solution. This, together with sufficient sterile distilled 

 water to make the moisture content up to 20 per cent, was thoroughly 

 mixed in the soil. Each series, together with sterile blanks, was incu- 

 bated at 28° to 30° C. for 21 days, and then the nitric nitrogen deter- 

 mined as follows {4, p. 200) : 



The contents of the beaker, together with 500 cc. of distilled water 

 and 2 gm. of alum, were placed in quart Mason jars and agitated for five 

 minutes in a shaker. 



An aliquot part (100 cc.) of the supernatant liquid was pipetted off, 

 and, together with 2 cc. of a saturated solution of sodium hydroxid, was 

 evaporated to about one-fourth of its original volume to free it from 

 ammonia. To this were added 50 cc. of ammonia-free water, 5 gm. of 

 "iron-by-hydrogen" and 30 cc. of sulphuric acid (sp. gr. 1.35). If less 

 than 40 mgm. of nitric nitrogen is to be determined, it is well to take a 

 correspondingly smaller quantity of iron and sulphuric acid. The neck 

 of the reduction flask was fitted with a 2 -hole stopper, through which 

 passed a 50-cc. separatory funnel and a bent tube which dipped into a 

 vessel containing water in order to prevent mechanical loss. The acid was 

 slowly added and allowed to stand until the rapid evolution of hydrogen 

 was over. It was then heated to boiling for 10 minutes. The contents 

 of the side vessel were returned to the reduction flask before the reaction 

 was complete, thus insuring the complete reduction of any nitrates 

 which may have been carried over with the first violent evolution 

 of the hydrogen. The contents of the reduction flask were transferred 

 to Kjeldahl flasks, neutralized with sodium hydroxid, and distilled into 

 standard acid. The excess of acid was titrated back with standard 

 alkali, lacomoid being used as an indicator; controls were made on all 

 the reagents, including the alum used as a flocculant. 



In every case at least four determinations were made with each con- 

 centration of the salt, and, in the absence of agreement between deter- 

 minations, the series was repeated so that the results as herein reported 

 are in every case the average of four or more closely agreeing determina- 

 tions. Hence, experimental error has been reduced to as near a mini- 

 mum as possible in this kind of work. 



The solutions of the salts were prepared by weighing gram-molecular 

 quantities of Merck's best grade of the respective salts into 1,000 cc. of 



