304
INDUSTRIAL AND ENGINEERING CHEMISTRY
SCALE
VOL. 11, NO. 6
2’. I’
FIGURE 1. DIAGRAM OF APPARATUS
the nitrogen content of the alloy. The excess of acid is titrated with standard 0.02 N sodium hydroxide solution. Two drops of a 1 per cent aqueous solution of sodium alizarin sulfonate are used as an indicator. The end point is marked by the complete disappearance of the clear yellowish green color, or the first indication of a brown. Each milliliter of 0.02 N hydrochloric solution is equivalent t o 0.00028 gram of nitrogen. A blank is run on all the reagents used and any nitrogen found is deducted. For steels containing very low percentages of nitrogen, solutions weaker than 0.02 N are used. Should the steel contain vanadium, titanium, columbium, tantalum, or any other metals known to form a nitride insoluble in hydrochloric acid the solution obtained as described in the first paragraph should be filtered on a 9-cm. filter and the residue washed well with 1 per cent hydrochloric acid. The nitrogen in the filtrate is determined as described in paragraphs 2 and 3. The paper and insoluble residue are transferred to a 500-ml. Kjeldahl flask, 10 rams of potassium sulfate, 1 gram of copper sulfate, and 20 mf of sulfuric acid (sp. gr. 1.84) are introduced, and the flask and its contents are heated just below the boiling point of the acid until all frothing ceases. At no time during the digestion should the part of the flask above the,surface of the liquid be heated. The liquid is next heated to boiling and the boiling continued for from 15 to 30 minutes after the solution has become colorless. The solution is allowed to cool, 200 to 250 ml. of ammonia-free water are added, the flask is connected to the condenser, 150 ml. of 10-per cent sodium hydroxide solution are added, and the nitrogen in this solution is determined a8 described in paragraph 3. A blank is run on all the reagents used, including the filter paper, and any nitrogen so found is deducted. Any nitrogen found after deducting the “blank’: is added to that obtained by acid solution of the sample and distillation, to obtain the total nitrogen. Ammonia-free water is prepared by dissolving 200 grams of potassium hydroxide and 8 grams of potassium permanganate in 1100 ml. of distilled water and boilin the solution until the volume has been reduced to a proximat& 1000 ml. This solution is added to the water to &e purified in the ratio of 1 to 10. Distillation is then carried on until a test of 100 ml. of the distillate does not require more than l or 2 drops of 0.02 N hydro-
chloric acid solution. Two drops of a 1 per cent aqueous solution of sodium alizarin sulfonate are used as the indicator.
Literature Cited Allen, A. H., J . Iron Steel Inst. (London), 8, 181 (1880). ( 2 ) Johnson, C. M., Iron Age, 134, (July 26, 1934). (3) Jordan, L., and Swindell, F. E., Natl. Bur. Standards, Sei. Paper (1)
45’7 iNov. 8. 1922). ~. .
Ruff, O.,and-Eisneg, F., Ber., 41, 2252 (1908). ( 5 ) Tsohischewski, N., J . Iron Steel Inst. (London), 92, Part 11, (4)
47-90 (1915).
( 6 ) Weiss, L., and Englehardt, T., 2. anorg. Chem., 65, 38-104 (1909). PRESENTED before the Division of Physical and Inorganic Chemistry a t the 97th Meeting of the Americitn Chemical Sooiety, Baltimore, Md.
Correction I n an article entitled, “A Modification of the Berl-Kullmann Melting Point Block” [IND.ENG. CHEM., Anal, Ed., 9, 340 (1937)] failure was inadvertently made to mention an article by Matthaus and Sauthoff [Chem. Fabrik, 8, 92 (1935)], who have designed a block in which reflections from the surface of the melting point tube are eliminated by illumination from above. Unfortunately, this article was not abstracted by the American or British abstracts, upon which dependence was placed in the literature search (an abstract was later found in Centralblatt), The author wishes to acknowledge the priority of Matthaus and Sauthoff in regard to the feature of the block mentioned. F. W. BERGSTROM STANFORD UNIVERSITY. CALIF. dpril 24, 1939
