PHYSICAL P R O P E R T I E S OF AMMONIA AND CITRIC ACID.
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test with the diphenylamine reagent as prepared by us is conducted as follows: Place I cc. of the liquid to be tested in a clean test tube; add I drop of the diphenylamine reagent and mix thoroughly by shaking. From a pipe is added 2 cc. of concentrated sulfuric acid, while the tube is held at an angle so as to form two layers of the liquids. The tube is gently agitated so as to cause a slight mixing of the liquids a t the plane of contact, and it is then placed in a bath at the temperature of 40’ and left for 15 or 20 minutes. This method will re\-ea1 the presence of one part of nitrite nitrogen in 25 million or one part of nitrate nitrogen in 35 million. By heating for one hour instead of 15 or 2 0 minutes the test will show one part of nitrite nitrogen’in 32 million or one part of nitrate nitrogen in 44 million. REFERENCES.
Ann. 132, 160.
* Ber., 5, 284. Jahresb. Tier-Chem., 1875,918. “Indicators and Test Papers,” 1907, p. 68. 5 “Principles and Practice of Agricultural Analysis,” I, p. 532. “Qual. Anal”., Trans., 1906, p. 388. Bull. soc. chim., 1889,350. * B u l l . S O C . chim., 1889, 670. Chem. News, 51, 41. l o Z.angew. Chem., 1894,345. l 1 Treadwell-Hall, “4nalytical Chemistry,” 1907,I, p. 340. l Z j .Chem. SOC. Abs., 50, 99 (1886). l 3 2. anal. Chem., 39, 429 (1899). W E S T RALEIGH. N.
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PHYSICAL PROPERTIES OF AQUEOUS SOLUTIONS CONTAINING AMMONIA AND CITRIC ACID. BY ROBERTA . H A L L A N D JAMESM. BELL. Received February 22. 1911.
In the analysis of commercial fertilizers for the so-called (‘available” phosphoric acid, it is usual to employ a solution of “exactly neutral” ammonium citrate,l having a specific gravity of 1.09 a t 20’. After extraction of the fertilizer with water, the residue is treated with the citrate solution and the phosphoric acid which remains undissolved is teimed insoluble, or non-available ; that which the water dissolves is the watersoluble; and that dissolved in the citiate solution is the reverted or citratesoluble. The sum of the water-soluble and the citrate-soluble phosphoric acid constitutes the available. Upon the results of these analyses depend the valuation of the fertilizer material, and, if the guarantee accompanying the fertilizer claims a higher percentage of phosphoric acid than is shown in the analysis by the state chemist, the manufacturer is liable to a fine. Bureau of Chemistry, Bull. 107 (revised), I.
GENERAL, PHYSICAL AND INORGANIC.
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I n the preparation of the (‘exactly neutral” ammonium citrate solution, however, great difficulty is encountered, due to the lack of sensitiveness of every color indicator. This lack of sensitiveness in the color indicator is general in the neutralization of a weak base, such as ammonium hydroxide, by a weak acid, such as citric acid. The Association of Official Agricultural Chemists prescribes’ the use of a saturated alcoholic solution of corallin as indicator in testing for the neutrality of the citrate solution; also an “optional method” wherein the citrate is precipitated by an alcoholic solution of calcium chloride, and the filtrate tested for acidity or alkalinity with cochineal as indicator. This method is employed apparently with the object of avoiding the difficulty experienced in determining the end point in the former method. That both methods are unreliable and unsatisfactory is evidenced by the .fact that at almost every meeting of chemists engaged in fertilizer analyses there is animated discussion of, and general protest against, both the ‘
