392
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 33, No. 6
Acknowledgment The author wishes to acknowledge the work of other members of the TVA chemical engineering staff in the develop ment of the procedures described in this paper.
Literature Cited (1) Brown, Morgan, and Rushton, IND. ENS. C~EM.. Anal. Ed., 9, 524-6 (1937). (2) Curtis, Miller, and Newton. Chem. Met. Eng., 45, 193-7 (1938).
P n ~ a n x ~ ebefore o the Dividon of Physical and InorgsniC Chemistry at the lCOth Meeting of the American Chemical Sooiety. Detroit, Mich.
Oxidation of Graphite in the Analysis of Ferrous Metals FIGURE 4. EXTRACTOR TJNITS Metal cans are electriaally heated water bat1hs. Conioal oover on third bath from left aids in heating sinimed-glass disk
about 2.5 to 3.25 em. (1 t o 1.5 inches) beLuwuuc uup. I L ~ ~ ~ U too vigorously will cause the acid t o creep over the edge, while heating too gently will fail to oxidize the phosphorus completely. The heating is continued until the solution volume is 2 to 3 ml. The solution is then cooled and neutralized, and the orthophosphate content is determined by a standard method. When the method given hy Brown, Morgan, and Rushton was used by the analysts in the routine control laboratory, considerable difficulty was encountered in obtaining check results from aliquots of the same benzene solution. The time allowed for completion of the action of the initial addition of the nitric acid-bromine solution and the subsequent rate of boiling the mixture apparently influenced the degree of oxidation of the phosphorus and the hydrolysis of the resultant oxides. The use of perchloric acid after decomposition of the copper-phosphide precipitate gives uniformly reproducible results. Table I shows the results obtained by two analysts using t h e modified procedure. Both analysts used aliquots of the same benzene solution of phosphorus. TABLEI. ANALYSISOF PHOSPHORUS Analyst
Phosphorus %
,
RALPH H. STEINBERG AN0 FRED WILSON SMITH Carnegie-Illinois Steel Corporation, South Works, Chemioal Laboratory, Chicago, Ill. L Y ~
I.
N T H E determination of manganese and phosphorus in
irons containing graphitic carbon it has been necessary to filter off the graphite after the sample is in solution. During solution water must he continually added to prevent the separation of gelatinous silica which would render the grsphite filtration difficult. With many irons these operations may require an hour or more. While perchloric acid will dissolve the sample rapidly, it oxidizes graphite only slightly. However, if 0.2 gram of sodium dichromate (or other soluble chromium salt) is added to the sample and the contents of the flask are fumed strongly, the graphite will be completely and rapidly oxidized. The chromium is subsequently volatilized quickly (2)by the addition of sodium chloride. A single determination for manganese can he made in 25 minutes, and 12 to 18 determinations in an hour. The method can also be adapted to the determination of phosphorus with at least two advantages. The use of nitric acid in conjunction with the usual hydrochloric-perchloric acid mixture has been found to eliminate the loss of phosphorus as phosphorus hydrides, and the rapid oxidation of the graphite saves much time as compared with prior procedures.
Procedure for Manganese
The sum of the benzene-soluble phosphorus and benzeneinsoluble residue seldom equals 100 per cent. The sample used to obtain data given in Table I contained 0.6 per cent benzeneinsoluble material. The difference of 0.4 per cent between 100 per cent and the sum of the benzene-insoluble material and phosphorus covers the inaccuracies of the method and unaccounted for substances such as silicon tetrafluoride and other compounds of flnorine soluble in phosphorus and benzene.
To a 1.000-gram sample (0.5 gram for over 1.25 per cent of manganese) in 8 500-ml. Erlenmeyer flask add 0.2 gram of solid sodium dichromate, 5 ml. of dilute hydrochloric acid (1to l),and 25 ml. of 72 per cent perohlano acid. Heat until dense white fumes issue from the mouth of the flask; then volatiliae the chramium by adding 0.5 gram of sodium chloride at short intervals until the red fumes cease to be evolved upon the addition of the salt. Remove the flask from the hot plate, let it cool somewhat, wash down its neck and sides with water, and again heat until its contents fume. When the flask cleam of white fumes (fumes will still form at the mouth), remove it from the hot plate. Add 3 ml. of 85 per cent phosphoric acid, 10 ml. of 0.8 per cent silver nitrate solution, 100 ml. of warm water, and 2 ml. of 25 per cent ammonium persulfate solution. Bail for 2 to 3 minutes to decompose peroxides. add 8 ml. of 25 per cent ammonium per-
ANALYTICAL EDITION
June 15, 1941
393
of dilute nitric acid (1 to 2). Boil for 5 minutes, cool t o room temperature, add 50 ml. of ammonium molybdate solution ( I ) , COW~ R I S O X OF MANGANESE DETERMINATIONS BY and let stand for 0.5 hour with occasional shaking. Finish as DIFFEREXT METHODS usual by filtering, dissolving the well-washed precipitate in Manganese Found excess alkali, and titrating the excess with standard nitric acid A. S. T M. method HClO~-NazCrz01-NaCl solution. Sample E30-39 ( I ) method A standard iron of an analysis similar to the unknown sample 70 should be carried through all the steps in order to standardize 1 60 the nitric acid. 0 79
TABLEI
1 12
Caution
0 85
0 14 0 23
TABLE11.
O F PHOSPHORUS DETERMINATIOSS BY DIFFERENT METHODS
C'O\lP.4RIsOS
Phosuhorue Found A 8 T. M.method HC104-NazCrzOv-SaCI
Sample Pig Pig Pig Pig
lion A , 4.57" C iron B , 4.57" C iron C, 4.5% C iron D, 4.5% C
E30-39 ( 1 ) % 0.205 0.198 0.177 0.073
method % 0.206 0.197 0.174 0.072
sulfate solution, and boil for 30 seconds. cool and titrate with arsenite solution (3.75 grams of sodium arsenite per liter), standardized against a standard steel or iron.
Procedure for Phosphorus To a 1.000-gram sample in a 500-ml. IMenmeyer flask add 0.2 gram of sodium dichromate, 10 ml. of dlilute nitric acid (1 to 2), 5 ml. of dilute hydrochloric acid (1 to l),and 25 ml. of 72 per cent perchloric acid. Heat until dense white fumes issue from the mouth of the flask and volatilize the chromium by adding 0.5-gram portions of sodium chloride as directed in the procedure for manganese. Remove the flask from the hot plate and allow it to cool. Add 40 ml. of water and 10 ml. of 20 er cent sodium hydrogen sulfite solution, twirl the flask, and a d s 10 ml.
Perchloric acid must be considered a hazard and handled with caution at all t.imes. If a bit of paper, oil, cloth, or other organic matt'er finds its way into fuming perchloric acid i t may cause a disast'rous explosion. So far the authors have encountered no difficulty when using these methods.
Conclusions Chromic acid in fuming perchloric acid oxidizes graphite completely. Xitric acid added a t the beginning of a perchloric acid phosphorus determinat'ion prevents the loss of phosphorus as hydrides. The solution of iron is hastened and the graphite is readily removed by the use of perchloric acid and a soluble chromium salt. Application of these methods to the determination of manganese and phosphorus in irons containing graphite gives results agreeing with the older methods and effects a time saving of 40 to 50 minutes.
Literature Cited (1) Am. Soc. Testmg Materials, "Methods of Chemical Analysis of t h e Metals", 1939. (2) Smith, F. W., IND. ENG.CHEY.,Anal. Ed., 10, 360-4 (1938).
A Simple Sintered-Glass Salt Bridge H. .4,, LAITINEN, University of Illinois, Urbana, 111.
Method of Construction
that of Bright and Miller ( I ) , often have the disadvantage of complexity of construction and tend towards high electrical resistance. bridge described here can be made of 3-mm. tubing if desired, is simple, has a low electrical resistance, and effectively eliminates siphon action. Thus it is unnecessary to maintain
CT
Pyrex glass is ground to a h e powder in a porcelain mortar. The 3- to 10-mm. Pyrex tubing to be used is sealed at one end and filled to a length of a few centimeters with the powdered glass. The glass pov,-der is warmed gently to allow expansion of the gases in it, and the glass is tapped to settle the powder in the end of the tube. The tubing is now heated with rotation, a t some distance from the end, in a very small oxygen flame. As soon as the tubing begins to soften it is withdrawn rapidly from the flame and suction is applied with the mouth partially to collapse the tubing. The end of the tube is cut off, and the excess powdered glass is removed. The sintered-glass membrane can be tested by suction. it should be dense enough so that water can barely be sucked through with the mouth. With practice the membranes can easily be constructed; the main difficulty is in preventing complete fusion of the powdered glass. The bridge is completed as shown in Figure 1. Either one or both ends may be provided with the sintered-glass diaphragm, and the stopcock may be omitted. The bridge is cleaned and filled by applying an aspirator or suction pump to the vertical arm, shutting off each end of the bridge in turn, if necessary, by means of R piece of rubber tubing provided with a clamp.
Literature Cited (1) Bright, W. M., a n d Miller, E. L., IND. ENCI.CHEII.,Anal. Ed., 9, 346 (1937). (2) Irving, G. W., and Smith, N. R., Ibid., 6. 480 (1934).
