INDUSTRIAL AND ENGINEERING CHEMISTRY
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lamp for 10 or 15 minutes, as would be done in the ignition of the magnesium pyrophosphate, the asbestos mat takes on a reddish tint due to the oxidation of the iron in it, and has
Vol. 16, No. 12
increased in weight a few tenths of a milligram. Obviously, this precaution should be observed in the preparation of the crucible.
T h e Interference of Ammonia with t h e Hypochlorite Reaction for Aniline' By E. S. West KENTCHEMICAL LABORATORY, UNIVERSITY orr CHICAGO,CHICAGO, ILL.
URING the course of a n investigation with Professor Stieglitz on the molecular rearrangement of sym-bistriphenylmethylhydrazine and monotriphcnylmethylhydrazine2 there was frequent occasion to test for the presence of aniline. The reaction of R ~ n g ewhich , ~ consists in the formation of a violet coloration upon the addition of calcium hypochlorite to a n aqueous solution of aniline, was employed as a test. Among the reaction products of rearrangement of the hydrazines, ammonia was often present in varying amounts. It was found that the presence of both ammonia and its salts greatly reduces the sensitiveness of the hypochlorite reaction for aniline. Experiments demonstrated that, as ordinarily carried out, the test is negative in the presence of very considerabe amounts of aniline if relatively small concentrations of ammonia or its salts are present. Under such conditions the solution tested generally becomes first yellow in color, then brown, and a brown amorphous precipitate separates. The interference of ammonia and its salts may be avoided by aerating the ammonia out of the solution before testing for aniline. If ammonium salts are present the solution is rendered slightly alkaline before aeration. Another procedure that may be employed successfully is to acidify the
D
.
Received May 26, 1924. West, Doctor's Dissertation, The University of Chicago, 1923,as yet unpublished. a Pogg. Ann., 81, 05; 32, 331 (1834). 1
2
solution slightly with hydrochloric or sulfuric acid before adding the hypochlorite solution. The test is not quite so sensitive under these conditions as in the absence of ammonia and its salts and with a neutral or alkaline solution. The color is more transient and not quite so intense. If the solution to be tested for aniline, and containing ammonia or its salts, is rendered very strongly alkaline with concentrated alkali before the addition of the hypochlorite, the interference is partly overcome. This procedure is not very good and does not compare with the others suggested.
EXPERIMENTAL Several experiments were performed in order to determine, a t least semiquantitatively, the degree of interference with the hypochlorite reaction for aniline occasioned by the presence of ammonia and its salts. These experiments were not carried out, as in laboratory practice, to obtain the greatest possible sensitiveness of the reaction. I n most cases much larger quantities of aniline and hypochlorite were used than ordinarily, and the hypochlorite was blown into the aniline solution quickly and mixed instead of being added drop by drop. An 0.8 M solution of sodium hypochlorite was employed in place of the customary bleaching powder solution, in order that a greater concentration of hypochlorite might be obtained in solution. It was reasoned that, by using rather high concentrations of hypochlorite and aniline, the magni-
INTERFERENCE O F AMMONIA WITH HYPOCHLORITE REACTION FOR ANILINE NaOCl CaHdNHa s o h . s o h . (2 mg. per cc.) (0.8 M ) NHs soh. (NHa)zSO4 NHiCl NH4Ac Has04 NaOH HIO NaCl Expt. Cc. Cc. Grams Cc. Grams Cc. Grams Grams N Cc. Grams Cc. Cc. Grams A 0.22
B
1.14
C
z
F
G H I
JKL
M N 0
P
Et S
T
Negative
1.3
Note 1. Negative Very faint-iimit of reaction
0.100 0.044 0.044 0.22 0.011
1.14 0.100 0.50
0.030 0.060
0.055
0.044
0.050
0.100
RESULT
0.5
1
Positive J
Note 2. Note 3. Note 4. Note 5. Negative Note 6 Note 7 Note 8. Note 9 Note 10
Positive Negative Negative Neaative
Negative
a T h e figures in parenthesis indicate the numerical order of mixing the reagents. NOTES: 1-With 0.055 gram (NH4)zSOd the reaction was faintly positive. 2-A violet color changing rapidly into red and reddish brown appeared. When the hypochlorite was added drop b y drop a much morecharacteristic reaction was obtained. 3-With 0.0055 gram NHa a positive test was obtained. 4-With 0.025 gram (NHn)zSO4 a positive test was obtained. 5-The addition of 0.15 cc. 0.8 M NaOCi solution t o the above mixture gave a positive test. When the reaction was repeated with 0.050 gram (NHdzSO4 a positive test was obtained. 6-The characteristic purple-violet color developed upon the addition of the hypochlorjte. After adding the (NHi)nSOa the color faded more rapidly than in case of a control mixture. When 1 gram of (NHI)PSOIwas added the color faded qulckly. 7-The characteristic color was destroyed in 5 minutes. 8-Moderate concentrations of NaCl do not interfere appreciably. Other salts a s KCl and CaClz act similarly. 9-The hypochlorite was added drop by drop and formed a layer on top of the mixture. T h e chsracteristic color appeared. The reaction was negative when the hypochlorite was quickly blown into the aniline salt mixture. 10-The hypochlorite was added as a layer underneath. Positive reaction a t the junction of the liquids, When t h e hypochlorite was blown quickly iato the aniline solution t h e reaction was negative.
I N D U S T R I A L AhTD ENGINEERING C H E M I S T R Y
December, 1924
tude of the interference of ammonia and its salts with the reaction would be more apparent than with the customary concentrations of these substances. The results of a number of experiments are shown in the table.
DISCUSSION AND SUMMARY The hypochlorite reaction as a test for aniline is interfered with by the presence of relatively low concentrations of ammonia and its salts (Expts. E and F). This inhibitory effect is largely avoided by making the solution to be tested slightly acid with sulfuric acid (or by hydrochloric acid) before adding the hypochlorite (Expts. G and H). The addition of a large amount of alkali avoids the interference of ammonia and its salts, but less satisfactorily than acidification (Expts. I and K). One of the most satisfactory procedures to avoid inter-
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ference is aeration of the ammonia out of the solution before the addition of the hypochlorite. If ammonium salts are present the solution should be made alkaline before aeration. The inhibitory effect of ammonia and its salts is due in part to their interaction with the hypochlorite4 (Expts. N and 0), and in part to their effect upon the colored product formed in the reaction (Expts. P and Q). The first interference predominates. Other factors may be concerned. Sodium chloride and other salts, when present in very high concentrations, interfere with the reaction (Expts. R and S). There is less interference with the reaction by ammonia, its salts, sodium chloride, etc., when the hypochlorite solution is added drop by drop to, or as a layer underneath, the aniline solution, than when it is added very rapidly and thoroughly mixed (Expts. S and T). 1 Raschig,
Bcr., 40, 4586 (1907).
Determination of Chromium and Vanadium in Steel’ By Leif Lindemann KONGSBERG VAABENFABRIK, RONGSBRRG, NORWAY
HROMIUM-VANADIUM steels cover a wide range of application in our “alloy age.” The following method for the determination of these metals in steel is founded on numerous estimations and includes points from the best of the modern methods. It is based upon the oxidation of chromium from the trivalent to the hexavalent condition in dilute sulfuric acid solution by means of persulfate and permanganic acid, the reduction of the chromic acid and the vanadic acid by means of ferrous sulfate, the estimation of the slight excess of ferrous sulfate by means of a standard chromic acid solution, followed by a titration of the vanadyl to vanadic acid by means of a standard potassium permanganate solution. Hydrochloric acid, nitric acid, and chlorine are not allowed to be present a t all and important sources of error are thus removed. The combination of persulfate and permanganic acid avoids the formation of large quantities of manganese dioxide. The retitration of the slight excess of Fe++ after the reduction to Cr+++ and V++++ has its main point in an elimination of all the Fe++, as this has three times the effect on vanadium as on chromium, but a slight excess of Cr+ +++ has no effecton the described determination of vanadium. It is thus impossible to determine chromium and vanadium directly by the electrometric method, as there will be some V present before all the Cr++++++is reduced, and the equilibrium is very slowly restored.
C
++
PRoCE DURE Weigh a 1-gram sample into a ~ ~ O - C C . low, , lipped beaker and add 15 cc. of a solution made by mixing 250 cc. of concentrated sulfuric acid with 750 cc. of water and 2 grams of silver nitrate. Cover with a watch glass and heat until the evolution of hydrogen ceases. Remove from the heat and add nitric acid (specific gravity 1.2) drop by drop (3 cc. for the high-speed steels and 2 cc. for the other steels) through the lip of the beaker, this being still covered, and boil the solution for 3 minutes. If a dark residue remains there may be rare chrome carbides in the steel (air-hardening armor plates after the Krupp procedure) or when cobalt is present unsoluble complexes are sometimes thrown out. The residue should then be filtered off, ignited, and fused with a small 1
Received July 12,1924.
amount of sodium carbonate and potassium nitrate and examined for chromium and vanadium. Remove the watch glass and evaporate the solution just at the boiling point until crystals of ferric sulfate can be observed; then more cautiously until the sulfuric acid fumes. Remove from the heat, cool, wash down the sides of the beaker with 25 cc. of water, and add about 2 grams of ammonium or potassium persulfate for the high-speed steels and stainless steels and about 1 gram for the other steels. Cover again, heat gently to boiling and boil for 2 minutes. If a pink color of permanganic acid is not observed, add drop by drop from a drop flask a 4 per cent solution of potassium permanganate until a slight permanent pink color is obtained; add 25 cc. of water and destroy the peracids by boiling. It is sometimes necessary to add a few drops of a 5 per cent manganese sulfate solution, but a slight excess of permanganic acid is ordinarily destroyed by boiling for 5 to 10 minutes and the orange color of chromate is observed a t the sides of the beaker by removing from the heat. Cool and allow the precipitate to settle, filter through a funnel prepared by putting 0.5 em. each of glass wool and asbestos in the cone, and wash several times with cold about 1per cent sulfuric acid until the volume of the filtrate amounts to about 150 cc., receiving it in a 300 to 500-cc. Erlenmeyer flask. Titrate with a N/15 to N/18 ferrous sulfate solution until the color just becomes green, then further in amounts of 1 to 0.5 CC., now using an approximately 2 per cent freshly prepared potassium ferricyanide solution as outside indicator. Determine the excess of ferrous sulfate solution by means of a N/173 potassium bichromate solution (0.2837 gram of the pure, pulverized, dried (at 130’ C.) salt per liter). As soon as the Turnbull’s blue appears to be less intense add the bichromate solution in portions of 1 to 0.5 cc. until the point is reached a t which no blue color appears after 30 seconds, using 5 drops (0.2 cc.) of the solution to determine the last end point. Titrate the solution with a standard potassium permanganate solution until a slight excess is stable for 3 minutes, and determine the excess of permanganate by titrating with the usual standard arsenic solution until the color just becomes bright green.
