I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Vol. 17, NQ.I
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solution tested in a 25.4-mm. (1-inch) cell with the tintometer was equivalent to yellow 3.00, thus showing that this steam treatment is not so effective in neutral as in acid solutions. It has been found possible to treat solutions of dark colored calcium salt after acidifying with sulfuric acid to make a 10 per cent acid solution. The calcium salts so obtained are pure white. TABLEI-LOVIBOZ~D READINGS FOR SOLUTIONS Cell Inches
SOLUTIONS TESTED Crude 5 solution of acid run Crude 5 F, solution neutralized with NaOH
Acid solution boiled up several times with charcoal Solution boiled up with charcoal several times and neutralized calcium salt solution Solution neutralized with NaOH: then steam-treated (once) Solution steam-treated; filtered calcium salt solution (once) Solution steam-treated; filtered (once)
'/16
'/I6 1/z
Yellow reading 4.00 4.00 3.60
1
8.00
1
3.00
1 1
1.70 0 . (water-white)
Experiments were carried out to ascertain whether or not the tarry matter coulg be hydrolyzed into an insoluble form which could he removed by filtering without using charcoal. These experiments were unsuccessful. After the steam treatment the solution was still highly colored, being only slightly lighter than before the treatment. This method has also been tried in a preliminary way for the removal of tar from naphtholsulfonic acids. The experiments so far carried out indicate that the soluble tar in naphtholsulfonic acid can be hydrolyzed by live steam in an acid solution in the presence of charcoal and thus be converted into an insoluble tar, which is removed by filtration. This method of removing the tar is limited, of course, t o sulfonation masses that contain no sulfonic acids capable of being hydrolyzed a t 100' to 130" C. The naphthalenesulfonic acids, which are easily hydrolyzed, however, are formed in low-temperature sulfonation where little or no tar is formed.
Determination of Aniline in Aqueous Solutions' By C. M. Carson GOODYEAR TIRE81 RUBBERCo., AKRON,OHIO
T
H E determination of aniline in aqueous solutions by colorimetric methods has been described.2J I n attempting to apply these methods to aqueous solutions of aniline of 0.1 to 3.0 per cent the color change was not found to be sufficiently delicate. For concentrations below 0.1 per cent the colorimetric methods are advisable. The potassium bromate-bromide method was tried, and although a fair degree of accuracy was obtained, the results were not so accurate or uniform as was hoped. The same may be said of the thymol blue method4 and the titration with sodium nitrate.5 An objection to the potassium bromate-bromide method is the use of starch-iodide paper, an outside indicator, which is not generally so accurate as an indicator in the solution. Furthermore, the use of starchiodide paper is slow as one must wait for the blue color to develop. Inasmuch as a rapid, accurate method was sought, an attempt was made to titrate aniline as the hydrochloride with 0.1 N sodium hydroxide using thymol blue indicator. This method had been in use in this laboratory for some time with varying degrees of success, but when tried on very dilute aqueous solutions the results were not uniform. If the solutions were turbid or colored it was impossible to match the yellow color of the standard aniline hydrochloride solution. Furthermore, on solutions of known aniline content the results with this indicator were found to be uniformly high. The titration of aniline as a base with 0.1 N sulfuric acid using Congo red indicator has been described by Julius.6 The characteristics of such a titration have been described by Hildebrand,' and by reference to his figures it will be noted that the break in the aniline curve occurs a t a pH value of 4. Hence, those indicators which change color in that range were chosen. They are as follows: bromophenol blue, pH 3 to 4.6; p-dimethylamidoazobenzene, p H 3 to 4; Congo red, p H 3 to 5; benzopurpurin, pH 2 to 4 ; tetraiodofluorescein, p H 4 to 5. Methyl orange, pH 2.9 to 4 is not a success in aniline titrations. 1
* 8
4 6
*
Received June 21, 1924. Elvove, THISJOURNAL, 9, 953 (1917). Christiansen, I b i d . , 11, 763 (1919). Clark and Lubs, J . A m . Chem. Soc., 40, 1443 (1918). Sabalifschka and Schrader, 2. angew Chem., 54, 45 (1921). J . Chem. Soc. (London), 63. 1,90A (1887). J . A m . Chem. Soc., S I , 847 (1913).
As will be shown, the first three indicators are superior t o thymol blue since they lie in the same pH range as aniline, whereas thymol blue changes from yellow to blue a t pH 3 or greater. Hence a larger amount of alkali is needed to neutralize the aniline hydrochloride and the results are high. The most successful indicators are bromophenol blue, p-dimethylamidoazobenzene, and Congo red, in the order named. They are all superior t o thymol blue and to the potassium bromate-bromide method. Some practice and the ability to note small color changes are necessary, but once this skill is attained the results are very accurate. The method is also applicable to the determination of the purity of commercial aniline, by dissolving a given weight in water and titrating an aliquot part of the water solution.. Experimental
Since aniline does not give a sharp end point with any indicator, it is necessary to use as a color standard a solution of pure aniline, enough 0.1 N sulfuric acid to neutralize i t exactly, and the same amount of indicator as used in the samples to be titrated. In using bromophenol blue the color standard is prepared by adding 3 drops of a 2.5 per cent alcoholic solution of the indicator to 10 cc. of a solution containing 2.05 grams of aniline per 100 cc. The volume is made up to 100 cc. and the calculated amount (22.05 cc.) of 0.1 N sulfuric acid to neutralize the aniline is then added. Ten cubic centimeters of the solution under examination are pipetted out into 100 cc. of watei, 3 drops of the indicatdr added, and 0.1 N sulfuric acid run in until the color of the standard is matched. The color change is from red to yellow, and it should be noted that with ordinary speed of titration the red color persists in returning after the end point is apparently reached. Hence it is necessary to add the sulfuric acid a few drops a t a time until this red color does not return. Results
Bromophenol blue is a remarkably accurate indicator, whereas thymol blue gives results so high as to be out o€ the question when small amounts of aniline are being determined. Below 0.1 per cent, aniline is in the field of colorimetric determinations and the method is no longer so accurate. Al-
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
January, 1925
though no figures are giver1 for larger quantities of aniline, the method is accurate for a 2.0 per cent solution and using 1 N sulfuric acid.
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Sample 1 2 3 4 5 6 7 8
Sample 1 2 3 4 5 6
7 8
TABLEI-BROMOPHENOLBLUEA N D THYMOL BLUE -BROMOPHENOL BLUEF-- T H Y M OBLUE L 0.1 N Aniline Aniline Aniline 0.1 N found Per cent found Per cent NaOH present HiSOa Gram Cc. Gram error Cc. Gram error 0,2052 22.05 0,2051 0.0 23.25 0,2162 5.3 0,1846 1 9 . 8 5 0,1846 0.0 22.4 0,2083 1 2 . 7 0.1642 17.70 0.1646 0.2 1 8 . 1 5 0.1689 2.8 0.1436 1 5 . 3 5 0,1428 0.3 15.5 0,1442 0.4 0,1231 1 3 . 2 5 0,1232 0.0 14.95 0,1390 1 3 . 0 0,1026 11.15 0,1037 1.0 12.5 0.1162 1 3 . 2 0.0821 8.75 0.0814 0.8 9.85 0.0916 1 1 . 5 0,0410 4.6 0,0428 4.4 7.25 0.0670 .. .
TABLE 11-POTASSIUM BROMATE-BROMIDE Per cent Aniline found Aniline present 0.1 N &SO4 Gram cc. Gram error 0.14 22.1 0.2055 0.2052 0.7 19.7 0.1832 0.1846 17.45 0.1621 1.3 0.1642 0.55 15.35 0.1428 0.1436 13.45 0.1261 1.6 0.1231 10.85 0,1009 t.6 0.1026 J.0 9.25 0.0860 0,0821 17.0 5.15 0.0479 0.0410 ~~
Somewhat more uniform results, although having a larger divergence from the known amounts, were obtained with p-dimethylamidoazobenzene. Eight drops of a 1 per cent alcoholic solution are used. The color change is from yellow to rose red, and approximate results may be obtained, as with bromophenol blue, without the use of a standard aniline solution. Such a standard is, however, advisable for accurate determinations. I n using this indicator the end point is marked by the entire absence of any yellow color. The rose red color when obtained may fade out; hence additional 0.1 N sulfuric acid should be added, 1 or 2 drops a t a time until the red color becomes permanent. Table I11 shows the results obtained with this indicator, a standard aniline solution being used for color comparison. Sample 1 2 3 4 5
6 7 8
TABLEIII-i?-DlMETHYL.4MIDOAZOBENZENE Aniline found Aniline present 0.1 N HzSOa Gram cc Gram 0,2055 22.1 0.2052 19.9 0,1846 0.1852 0.1637 17.6 0.1642 0,1432 15.4 0.1436 0,1223 13,l5 0.1231 0,1037 11,l5 0.1026 0,0842 0.0821 9.05 0,0410 0.0451 4.85
.
Per cent error 0.1 0.3 0.3 0.3 0.6 1.0 2.0 10.0
The definite increase in percentage error may mean that this is a more satisfactory indicator than broinophenol blue, in that an error curve may be plotted for reference. The results with Congo red (Table IV) were found to be more accurate than with thymol blue, but less so than with the other two indicators. The details of the Julius procedure are unknown to the writer, but good results were obtained by use of the following precautions: A standard aniline solution is absolutely necessary and the same amount of indicator must be used in both standard and unknown. It is well to use beakers of the same size and free from irregularities. The use of'Nessler tubes increases the accuracy somewhat. The titrations were made in the same may as the previous determinations, 5 drops of 1per cent Congo red solution in water being used. It should be noted that the end point of Congo red with aniline is marked by the complete removal of any reddish tinge and the appearance of a definite purple color in the solution. IV-CONGO RED TABLE Sample 1 2
3 4 5 6
7 8
Aniline present Gram 0,2052 0.1846 0.1642 0,1436 0.1231 0,1026 0.0821 0.0410
0.1 N &SO4 cc. 21.9 19.9 17.8 15.5 13.0 10.9 8.4 4.3
Aniline found Gram 0.2037 0.1851 0.1655 0,1442 0,1209 0,1014 0,0781 0,0400
Per cent error 0.7 0.2 0.8 0.4 1.7 1.1 4.8 2.4
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Results with Toluidines Since such favorable results were obtained with aniline, it was thought that equally good results might be secured with the toluidines.
Sample 1 2 3 4
Sample 1 2 3 4
TABLE V-BROMOPHENOL BLUE o-Toluidine o-Toluidine present 0.1 ' h &SO4 found Gram cc. Gram 0.0500 4.50 0.0481 0.1000 9.35 0.1000 0.1500 13.95 0,1492 0.2000 18.7 0.2000
Per cent error 3.8 0.0 0.5 0.0
TABLEVI-~~-DIMETEYLAMIDOAZOBENZENE Toluidine Toluidine present 0.1 N HnSO4 found Per cent Gram cc. Gram error 9.35 0.1000 0.0 0.1000 14.25 0.1525 1.6 0.1500 18.6 0,1990 0.5 0,2000 0.2500 23.0 0.2461 1.6
The results with p-toluidine were less favorable owing to its slight solubility in water, which made it necessary to use large volumes of the aqueous solution, and thus increased the possibility of error. Acknowledgment Thanks are due L. B. Sebrell for assistance in the preparation of this paper, and to C. W. Foulk, of Ohio State University, for his criticism of the manuscript.
Water Circulation Device'
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By Robert E. Jefferson 70 LINWOODR O A D HANDSWORTH, , BIRMINGHAM, ENGLAND
r
T sometimes happens that a circulation of water is desired through a vessel not provided with an outlet, and
perhaps from some cause it is impossible to make a suitable aperture to run off the water. The apparatus shown in Fig. 1 was designed by the writer in such a case.
L
3
A FIG.1
lF
A is the vessel through which the water had to circulate. B is the inflow tube coming from an elevated constant head apparatus, C. Water also flows from C through tube D to the automatic siphon E and fall tube, F . G is a hole-not too small-in the siphon E and situated a t the desired water line. H is the waste water from the constant head C. J is the supply. It is important that tube B is slightly higher than D. This apparatus was slightly modified to wash the mercury surface in the mercury bath of a Bone and Wheeler gas analysis apparatus. 1
Received September 26, 1924.
