March. 1924
I N D USTRIAL A N D ENGINEERING CHEMISTRY
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Soluble Aluminium and t h e Hematoxylin Test in Filtered Waters’ By William D. Hatfield CITYWATERDEPARTMENT, HIGHLAND PARK,MICH.
fades rapidly, but the color ECENT studies2 on The minimum solubility zone for aluminium hydroxide in carcompound formed a t p H 8.0 the presence of solubonate and bicarbonate solutions extends approximately from p H to 8.5isverypronoumedand ble aluminium in me5.7 to 7.3. Where water filtration plants use aluminium sulfate; quite permanent. These chanically filtered waters and operate so that the pH of the treated water falls near the limits data show very clearly that which have been coagulated of or outside of this zone, the efluent will in all probability contain while hematoxylin is an “inwith aluminium sulfate have soluble aluminium (“residual alum”). dicator” it also gives, a t p H shown that the insolubility The graoimetric test for this aluminium is tedious and is com8.0 to 8.5,distinctlydifferent zone for aluminium hydroxplicated by the naturally occurring aluminosilicates. I t is not colors in the presence and ide is approximately from suitable as a routine test for the aoerage waterworks laboratory. absence of aluminium ions. p H 5.7 to 7.3. When the The modified hematoxylin test presented here gioes results that Therefore, the hematoxylin pH value of the coagulated are accurate to 0.1 p . p . m. aluminium. The modification consists test for aluminium in filtered or filtered water is less than in forming the hematoxylin-aluminium color compound in samples waters must be made on pH 5.7 or more than 7.3, of water which haoe been adjusted to pH 8.2 to 8.3 and then acidifying samples which are buffered unprecipitated aluminium the color solution to p H 4.5. to a constant hydrogen-ion is found by the gravimetric concentration. method of analvsis. If extreme care is used to remove silica3 completely, the TABLEI gravimetric method determines the amount of alumina COLOR PRODUCED COLORPRODUCED ON originally present in the water plus any unprecipitated alupH O F BUFFER WITH HEMATOXYLIN NO ADDITION OF 0.37 SOLUTIONS A I + + +PRESENi P. P. Y. A L + + + minium from the aluminium sulfate, thus requiring two de14.0 Laoendet Green terminations to detect the presence of an excess of aluminium 12.0 Red Red i i . 0 Orange Orange in the filtered water. As these operations are not well fitted 9.0 Orange-yellow Orange-yellow 8 . 5 Red Purple for routine work in a waterworks laboratory, it is highly 8.0 Pink (lavender tint) Laesndn-flurfllc desirable to have a rapid colorimetric method which is sensi5.5 Yellow Yellow Yellow 2.4 Yellow tive to aluminium ions, and not to the alumino complexes which are present in the raw water. Concentrated aqueous solutions of numerous phosphates, Atack’s4 method for determining aluminium with Alizarin S (red) has not given very satisfactory results in the hands carbonates, oxalates, and acetates were studied to determine which buffer salt gave the best results in adjusting samples of numerous investigators. The logwood or hematoxylin color reaction with aluminium of lake water with pH values from 3.0 to 8.0 to a constant ions is so pronounced that it offers possibilities worthy of hydrogen-ion concentration, and also which buffer salts gave study. The most serious objections to the hematoxylin the best final hydrogen-ion concentration for the aluminium test for alum have been, first, that hematoxylin is an indicator color formation. The aluminium-hematoxylin color compound does not and hence is subject to variations in color with changes in hydrogen-ion concentrations; and second, that other ions form in buffer solutions more acid than p H 6.0 unless the produce colors with hematoxylin which would interfere. concentration of aluminium is relatively high. I n solutions The experimental work described below sustains these two more alkaline than p H 8.5 the color fades rapidly, while objections to the test as it has often been made, but presents between pH 6.5 and 7.5 the color formation is slow but a modified hematoxylin method which overcomes these oh- relatively permanent. Between p H 8.0 and 8.5 the most jectiorxs and is very satisfactory for routine water analysis. rapid and satisfactory color formation is obtained. The data in Table I1 illustrate the buffer action of three of the EXPERIMENTAL WORK most promising salts tried. The most satisfactory buffer I n Table I are shown the maximum color changes which and technic was found to be 1 ml. of saturated ammonium take place when an aqueous solution of hematoxylin is added carbonate (ammonium carbonate-carbamate) solution in to buffer solutions ranging from 2.4 to 14.0 pH units. To a 50-ml. sample of water. these buffer solutions containing hematoxylin, 0.37 p. p. m. SAMPLRS TO aluminium was added and a distinct color change took TABLE11-EFFICIENCYOF BUFFERSOLUTIONS IN ADJUSTING A CONSTANT pH place a t pH 8.0 to 8.5 and a t p H 14.0. The aluminium(Technic: 1 ml. buffer solution t o 50 ml. sample of water) hematoxylin color compound which is formed a t p H 14.0 pH AFTER ADDITION OF BUFFERTO SAMPLE
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Presented before the Division of Water, Sewage, and Sanitation a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 to 14, 1923. a Baylis, J . A m . Water Works Assoc., 10, 365 (1923); Daniels, Eng. News-Racord, 91, 93 (1923); Hatfield, paper presented before the 43rd Annual Convention of the American Water Works Association, May, 1923; Miller, paper presented before the 43rd Annual Convention of the American Water Works Association, May, 1923. 8 Buswell, Discussion at the 43rd Annual Convention of the American Water Works Association, May, 1923. 4 J . SOC.Chem. I n d . , 84, 936 (1915). 1
M1. 0.2 N Hzs04 pH of 10% per 1000 MI. Treated Water Ammonium Raw Water (Colorimetric) Acetate 6.7 8.1 0.0 6.7 7.5 0.5 6.77.3 1.0 6.66.9 2.0 6.5 6.6 4.0 6.6 5.9 6.0 6.65.58.0 6.53.5 10.0 Hematoxylin Variable Slow but color constant formation
Saturated Sodium Acetate 7.47.4 7.37.2 7.0 6.8 6.8 6.5Variable
Saturated Ammonium Carbonate 8.28.28.28.2 8.2 8.2 8.2 8.2 Rapid and constant
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
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The pure aluminium-hematoxylin color, in solutions made alkaline with saturated ammonium carbonate solution, is blue, but if there is a n excess of hematoxylin, which is red in this solution, the combination of red and blue produces the lavender or purple tint usually reported as characteristic of aluminium. When acid is added the excess hematoxylin turns yellow and the aluminium color compound turns purple. Combinations of these two colors give gradations of color from yellow through brown to purple. .Hematoxylin was tested for its color reaction with salt solutions which represented the ions commonly found in natural waters. The data in Table I11 show that the solutions of alkaline salts give a red color with hematoxylin, the intensity depending on the hydrogen-ion concentration, and that neutral and acid salt solutions and distilled wate (pH 5.8)give a yellow color. All these salt solutions, except those containing magnesium, ferrous, and ferric ions, turn red when made alkaline (pH 8.2) with 1 ml. of saturated ammonium carbonate solution. These solutions turn to a lavender color which is very similar to that produced by aluminium ions when treated in a similar manner.
Vol. 16, No. 3
The data in Table IV were obtained on acidulated samples of Lake St. Claire water and show the effect of the hydrogenion concentration of the water on the color formed with hematoxylin both with and without the presence of aluminium ions. The samples in Columns 4, 5, and 6 were treated with an equivalent of 0.27 p. p. m. aluminium. Column 4 shows the variation of color due to the variation in hydrogenion concentration, and Columns 5 and 6 show how satisfactorily the addition of buffers, according to the technic described below, brings the colors to a constant shade. The solutions and procedure for this modified hematoxylin method for aluminium in filter plant effluents are as follows:
REAGENTS-(~)Dissolve 0.1 gram C. P. hematoxylin (white crystals) in 100 ml. of boiling distilled water. This solution is stable for 2 or 3 weeks. ( 2 ) Saturate 500 ml. distilled water with ammonium carbonate and keep the solution in a glass-stoppered bottle in presence of an excess of crystals. (3) Prepare a 30 per cent acetic acid solution by diluting glacial acetic acid with distilled water, (4) Prepare a standard ammonium alum solution by dissolving 0.8366 gram of ammonium alum in distilled water and dilute to 1000-ml. One milliliter of this solution in 50 ml. of distilled TABLE111-COLOR REACTION O F S O M E SALT SOLUTIONS WITH HEMATOXYLIN water is equivalent to 1.0 p. p. m. aluminium. Use also a 1: 10 -ACID AND NEUTRAL-ALKALINEdilution of this standard solution. SOLUTION COLOR SOLUTION COLOR RC1 KHzPOd NaCl
Yellow Yellow Yellow
NHLl
Yellow
FeSO4("2) zS04 FeSOI MgSOi MnSOd CaCla Distilled water
Yellow Yellow Yellow Yellow Yellow Yellow
KOH KaHPO4 NaHCOs NazCOs NaOH NHiOH (NHdzCOa
Red Red Red Red Red Red Red
Ca(0H)z
Red
lavender tinge) {fades) (fades) (lavender tinge)
On acidification of the solution containing the magnesium color with 1 ml. of 30 per cent acetic acid, the lavender color is destroyed and does not interfere with the aluminium color formed under the same conditions. Tests with ferrous and ferric ions indicate that, in solutions buffered with ammonium carbonate, iron will interfere in concentrations greater than 0.1 to 0.2 p. p. m., but on acidifying the solution with 1 ml. 30 per cent acetic acid (resulting pH 4.5) the interference is not serious until a concentration of 1.0 p. p. m. of iron is reached. Summarizing, small amounts of aluminium plus hematoxylin a t pH values less than 6.0 do not produce readable color changes, but amounts as low as 0.05 p. p. m. aluminium, if treated with hematoxylin at p H 8.2 (more or less) and subsequently acidified, do give readable colors which are not subject to interference from other ions normally found in natural waters.
PROCEDURE-TO 50 ml. of water (to be tested) contained in a tall-form Nessler tube add 1 ml. of a saturated solution of ammonium carbonate and 1 ml. of hematoxylin indicator solution. Mix by inverting tube twice. Let the tube stand 15 minutes for the maximum lavender color to form, and then acidify with 1 ml. of 30 per cent acetic acid. Compare the color formed with that of standard color tubes which were prepared in exactly the same way and a t the same time by using standard ammonium alum solution and distilled water to represent from 0.0 to 1.0 p. p. m. aluminium. With concentrations less than 0.15 p. p. m. aluminium the color is compared against white paper through the length of the Nessler tubes, but with higher concentrations than 0.15 p. p. m. the color is best compared through the sides of the tubes.
The color standards should be made as nearly as possible a t the same time as the unknown color tube, because the color varies with time of formation. A difference of 15 minutes will make some difference in the tint, but will allow readings to 0.1 p. p. m. Color standards prepared with distilled water were satisfactory with the Great Lakes water, but if, because of interfering ions, the raw water does not compare with the zero distilled water standard, the standards should be made with raw water which has been filtered through a Berkefeld filter. I n this way any naturally occurring ions which interfere with the aluminium-hematoxylin color are compensated for in the standards. Care must be taken that the Berkefeld filter does not become contaminated with alum dust from the plant. Obtained by the gravimetric Many comparisons Of TABLE IV-EIWECT OF HYDROGEN-ION CONCENTRATION ON HEMATOXYLIN COLORSIN LAKE ST. CLAIREWATER method and the modified hematoxvlin method have been 0.27 P. p. m. made on filtered water samples with hydrogen-ion concenAluminium Column 5 I MI. Acidified trations ranging from 3.3 to 9.0 p H units. The comparisons 1 M1. Hem- 0 . 2 7 P . p . m . (NHdzCOa with 1 MI. Ml. 0.2 N show that the results check very satisfactorily where the Aluminium lM1.Hema30% Acetic Has01 per pH of. Treated 1000 M1. in 50-MI. plus Hematoxylin Acid p H values of the samples were above 6.0. Samples of the Sample toxylin (pH 8.2) (pH 4.5) Sample Water (4) (5) (6) filtered water with pH values below 6.0 very rapidly dissolve (3) (2) (1) Lavender- Yellowish silica from the ordinary flint glass laboratory sample bottles. Red Blue 7.8 0.0 Lavenderblue This is particularly true as the acidity increases. Unless Pink Blue 7.5 0.5 brown I blue special precautions are taken to remove all silica, the graviYellow- Lavender Lavender- Yellowish 7,. I 1.0 pink blue brown metric results on these acid samples are high. The modified Faded ender la"Lavenderblue 2.0 6.8 hematoxylin method gave very consistent results on acid Yellow More faded Lavender- Yellowish samples, which compared closely with the theoretical amount 4.0 6.5 lavender blue brown Yellow More faded Lavender- Yellowish of aluminium ions added. Near the two extreme ends of 5.9 6.0 lavender blue the aluminium hydroxide insolubility zone (pH 5.7 to 7.3) Yellow More faded Lavender8.0 5.8 lavender blue brown the hematoxylin method is more sensitive than the graviLavender- Yellowish Yellow Yellow 10.0 3.5 blue brown metric method.
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