1913] Burgess: Eeduction Methods for Soil Nitrates 53 



Escot^" utilizes aluminum filings, mercuric chloride and a solution 

 of potassium hydrate. J. T. Bornwater^^ uses aluminum filings 

 and a solution of potassium hydrate. 



Still further elimination was thus necessary among the reduc- 

 tion methods. The modified Ulsch method presented certain 

 difficulties of technique which, in the case of numerous deter- 

 minations, would render the method impracticable. The alumi- 

 num reduction method has been heretofore used successfull^y in 

 water analysis,^^ and it appeared advisable to make a study of 

 it as applied to determinations of large amounts of nitrates as 

 met with in soil work; it further seemed important to determine 

 the feasibility of its use for a large number of determinations 

 made simultaneoiLsly. Such other factors also as the amounts 

 of aluminum and of alkali to employ, the length of time, and the 

 temperature for reduction, demanded a careful test. 



Description of the Method 



One hundred grams of the soil in which the nitrates are to 

 be determined are placed in round-bottomed, enameled cereal 

 dishes which have a capacity of about 800 c.c. INIortars were 

 used at first, but the cereal dishes were found to be much lighter, 

 easier to manipulate, and less expensive. Two grams of pow- 

 dered CaO and exactly 200 c.c. of distilled water are added to 

 each dish. The contents of each dish are now thoroughly ground 

 and mixed with a pestle for from 3 to 5 minutes, after which 

 the soil and clay are allowed to settle for 15 or 20 minutes, and 

 are then filtered through paper. It may be said here that the 

 solutions should never be allowed to stand over 2 to 3 hours, as 

 there occurs a noticeable loss of nitrates, possibly due to dentri- 

 fication. In case it is impossible to proceed at once with the 

 determination a few drops of chloroform^ ^ may be added. One 

 hundred c.c. portions of the filtrates, obtained as above described, 

 are placed in 400 c.c. casseroles and 2 c.c. of a 50 per cent NaOH 

 solution, free from nitrates, added to each. These are then boiled 



10 Ann. Chim. Analyt. 14 (1909), 12, pp. 445-446. 



11 Chem. Centbl. (1906), I, 8, p. 703. 



12 Amer. Jour. Pub. Hyg., vol. XIX, 3. p. 1. 



13 V. I. Sazanov, Abs. in Centbl. Zuckerindus. 15 (1907),' 34, p. 923. 



