T H E PHYSICAL CHEMISTRY O F COLOR LAKE FORMATION. 111. ALIZARIK LAKES BY HARRY B. WEISER AKD EVERETT E. PORTER
Alizarin or dihydroxy anthraquinone is the most, important, mordant dye. I t was formerly obtained from the roots of madder, a plant of Indian origin, which was cultivated largely in France and in Holland before its synthesis from anthracene was accomplished in 1868. The chief mordants for the dye are alumina which yields a red lake, chrome which yields a reddish brown, tin which gives an orange, and iron which gives purple or black. If the fiber is treated with the so-called sulfonated oils before niordanting with alumina, there results the brilliant Turkey-red, a color reinarkable for its fastness to light and to the action of soap and water. Since, in general, alizarin is not taken up by alumina in the absence of calcium, the lake is usually assumed to be a calciuni aluminum alizarate.' I t is claimed that strontium, barium, and niagnesiuni may be substituted for calcium but the former are not satisfactory. Davison' found that hydrous alumina prepared from aluminum acetate takes up more alizarin in the absence of calcium salts thzn that prepared from the sulfate. Since the alumina mordant bath is aluminum sulfate, Bancroft3 concludes thab the function of the calcium i s not to fix the alumina on the fiber or the dye to the mordant but to remove sulfate which cuts down the adsorption of alizsrin. If this were true, soluble barium salt would be more satisfactory than calcium salt. -1s we shall see, the function of calciuni ion is to increase the adsorption of alizarin ion and not to cut down the concentration of sulfate. Biltz' was the first to suggest that the alizarin lakes might not be definite chemical compounds. Thus with hydrous chromic oxide the amount of alizarin Sly taken up incresses continuously with increasing concentration of solution showing no indication whatsoever of the formation of chromium alizarate. On the other hand, with hydrous ferric oside there was a rather marked increase in the amount of alizarin taken up with relatively small change in the equilibrium concentration, leading Riltz to conclude that iron and alizarin combine in the ratio of one molecule of FesOBto three molecules of alizarin. But the amount of alizarin taken up by the iron oxide is far in excess of that necessary to form alizarate, hence one is confronted by the necessity of assuming either that alizarate adsorbs the excess of dye or that the whole phenonienon is a case of adsorption of the dye by the oxide. Recently the iron and aluminum lakes of alizarin have been investigatd in J. SOC.Chem. Ind., 5 . 52j (18861 J. Phys. Chem., 17, 737 ' 1 9 1 3 ) . J. Phys. Chem., 18. I (1914). Ber., 38, 4143 (1905).
PHYSICAL CHEMISTRY O F COLOR LAKE FORMATIOS
1825
Rancroft's laboratory' and the conclusion reached that the lakes are adsorption complexes of sodium alizarate and the hydrous oxides of the iron and aluminum respectively. Since this conclusion could not be reconciled with our observations on the taking up of dyes by the hydrous oxides, a systematic investigation of the alizarin lakes and the factors influencing their formation was undertaken. Experimental Procedure X s in earlier experiments the metallic mordants, ferric oxide, chrome, and alumina were prepared as sols. These were precipitated by the addition of the alizarin dye, sodium alizarate or alizarin SW, at varying hydrogen ion concentrations and the adsorption determined from the change in the concentration of the supernatant solution. The hydrogen ion concentration mas varied by the addition of varying amounts of either sodium or potassium hydroxide or hydrochloric acid. Since alizarin is not affected by the hydrogen electrode under the conditions of the experiments, the initial and final pH values were determined accurately. ilnnlyszs of Alzzarzn. The accurate determination of alizarin and its simple derivatives called for a special investigation, since Knecht's method of titration with titanous chloride was found to be unsatisfactory. The procedure adopted consists in getting favorable conditions for the oxidation by permanganate of alizarin to phthalic acid without the precipitation of any manganese dioxide. In working out the experimental details, the quantity of dye was varied between 0.01 and 0.001millimoles, this being the approximate range of quantities to be analyzed in the adsorption experiments. The following procedure was found to be satisfactory: To the solution containing the alizarin in about 2 5 cc is added 5 cc of concentrated sulfuric acid and 2 cc of 31'2 manganous sulfate. To this solution, boiling hot, is added Si50 potassium permanganate avoiding an excess of more than one cubic centimeter at any stage of the titration. The addition of the potassium permanganate, a little at a time, is continued until there appears to be no further reduction after boiling for from 20 to 3 0 seconds in the presence of an excess of from one half to one cubic centimeter. A little practice enables one to tell from the color of the solution when the proper excess of reagent has been added. If the excess is much more than I cc, manganese dioxide is precipitated and if too small the oxidation is incomplete. After the oxidation is complete, the solution is cooled to about io" and R small excess of oxalate added. Potassium permanganate is again run in to the usual end-point. Some representative data on the accuracy of the method for the conzentrations used in this work are given in Table I. The suitability of the method was not tested for large quantities of dye. The theoretical equivalent/molar ratio is 2 6 , provided the reaction goes quantitatively to phthalic acid, carbon dioxide, and water. The observed ratios are low but consistently so. No other method was found which compares at all favorably with this one for the determination of such small quantities of the alizarins. Bull and Adams: J. Phys. Chem., 2 5 , 6 6 0 (1921); Williamson: 2 8 , 891 (1924).
1826
HARRY B. WEISER AND EVERETT E . PORTER
TABLEI Titration of Alizarin with Potassium Permanganate Cc 0.0006 M soln. alizarate titrated
normal molal ratio
Cc N / j o KhInOl required
20
23.3' 23.5 23.4
20
20
5 5
20.2
5
20.3 23.4
21.8
2
The Adsorption of Alizarin SW The sodium salt of alizarin mono-sulfonate was chosen for the initial experiments for several reasons: I t is easy to determine quantitatively even in small amounts; it is not reduced a t the hydrogen electrode in dilute solution; its acid is sufficiently soluble that no precipitation takes place throughout a wide' pH range; and finally, it is readily purified and weighed. Adsorption by Hydrous Chromac Oxide. The data for the adsorption of alizarin SW by hydrous chromic oxide at varying hydrogen ion concentrations is shown in Table I1 and represented graphically in Fig. I . The pH curve for the acid and alkali alone in the same total quantity of water is also given. The length of a horizontal line drawn from any point on the curve for the pH
TABLE I1 Adsorption of Alizarin S W by Hydrous Chromic Oxide at varying pH Values Cc of soln. mixed with 5 cc of sol containing 0.0125 gram of CrrOsin a total of 20 cc 0.0
HCf
N
0.037
I\'
KOH
2 . 5
0
1.5
0
1.0
0
0.j
0
0
0
0
0.57
0
1.13
0
2.27
0
3.39
Adsorption value in millimoles alizarin SW per gram Cr203
5 5 5 5 5 5 5 5 5
pH values
without dye or colloid
31 dye
0.01
2.46 2
total mixture
2.400
2.419 2.717
2.727
2.822
2.873 4.173 5.490
3.042
2.86
40
2.32 2.18 I . 70 1.41
without c o 11o id
3
11
1.15
7.554
0.16 0.09
10.529
4.478 6.170 7'556 9.283
10.634
10.44j
10.62
11.17
of the mixture without the colloid to the acid-alkali curve, gives the quantity of acid or base reacting with the dye. The curve is continuous giving no indication of the formation of a compound at any p H value. As would be expected, there is quite a buffer effect in the titration of the mono-sodium to the di-sodium salt. Moreover, there is a corresponding holding up of the
PHYSICAL CHEMISTRY O F COLOR LAKE FORMATION
1827
adsorption-concentration curve in this region. This has two causes: the concentration of the hydroxyl ions is not increasing in proportion to the alkali added; and, a t the same time, the concentration of the highly adsorbable dye ions is rapidly increasing. Just as was found in the case of sulfate and of oxalate,' hydroxyl ion may completely displace the dye, the latter requiring a slightly higher hydroxyl ion concentration than the former. This indicates that the dye is more strongly adsorbed than either sulfate or oxalate but is not SO strongly adsorbed as hydroxyl.
Adsorptzon by Hydrous Alumina. The observations on the adsorption of alizarin S R by hydrous alumina are given in Table I11 and plotted in Fig. I . Since the adsorption capacity of the alumina is much less than that of chromic oxide, a larger sample of the former was used in the adsorption studies. The graphs show the same general effects of the hydrogen ion concentration as was pointed out in the case of the chromic oxide, the difference being that the effects are leas pronounced with alumina thsn with chromic oxide in both the acid and basic baths. Here also, there is no indication of compound formation between the dye and the mordant at any hydrogen ion concentration investigated. It was found impossible to study the adsorption of alizarin S R by hydrous ferric oxide through a wide range of pH values, since the pH value zone in which the precipitation of the sol is complete, is very narrow in the presence of a constant amount of dye, and the accurate determination of the hydrogen ion concentration is impossible when the removal of the iron is incomplete. As would be expected, the zone of complete precipitation shifts toward the acid range with increasing concentration of dye duz to the strong adsorption of J. Phys. Chem. 31, 0000
(192;).
I 828
HARRY B. WEISER AND EVERETT E. PORTER
TABLE 111 Adsorption of illizarin SW by Hydrous Aluminum Oxide a t varying pH Values Cc of s o h . mixed with 5 cc of sol containing 0.0179gram of A1208 in a total of 20 cc
pcjN
0.037 N
KOH
Adsorption value in milliomoles alizarin SW per gram ALOs
0.01 M
pH values
dye
without dye or colloid
2.86
2 .j
0
0
2.0
0
1.5
0
5 5
1.0
0
5
0.5
0
5
0
0
5
0
0.57
5
0
I . 13
5
0
2.27
0
3.39
5 5
without colloid
totalmixture
2.400
0.98 0.90 0.86 0.66 0.61 0.41 0.26 0.22
2.722 3.11
2.873 4 . 173
10.62
11.17
5.490 7,554 10.529 I O .634
2.345 2.799
3.361 5.097 6.384 7.915 9,931 I O .896
the dye anion. The ease of reversibility of the ferric oxide sol will corne up again in some observations to be reported in a later section.
Adsorption of Alizarin Since the anion of alizarin SW is adsorbed by basic mordants giving color lakes whose composition is indefinite, depending on the concentration and p H value of the dye bath, there seemed to be no reason for believing that alizarin would react with ferric oxide to give ferric alizarate as Biltz believed. Bull and Adams' shook up a solution of sodium alizarate with ferric oxide and concluded that ferric alizarate was not formed since the hydroxide equivalent to the alizarate was not set free as would happen if a double decomposition reaction took place. The absence of any appreciable quantity of alkali in the bath led to the further conclusion that the lakes are adsorption complexes between ferric oxide and sodium alizarate. Similar conclusions were reached by Williamson2 with reference to the alumina-alizarin lakes. It was difficult for us to see how this conclusion could be correct for all of our observations showed that when the hydrous oxides are brought in contact with highly ionized salts which yield a strongly adsorbed anion, it is the anion and not the molecule of the salt which is adsorbed. To settle this question the following experiments were carried out: Pure sublimed alizarin was dissolved in the theoretical amount of sodium hydroxide to give sodium alizarate and the solution diluted to give a M/IOO solution of the salt. Preliminary experiments were carried out to determine the maximum ratio of sodium alizarate to oxide which could be used and still have a nearly exhausted bath. J. Phys. Chem., 25, 660 (19zij.
* .I. Phys. Chem., 28, 891 (1924).
PHYSICAL CHEMISTRY O F COLOR LAKE FORMATION
1829
For the chromic oxide sol, 113 cc containing 1.42 grams of CrzO3was required to decolorize 100 cc of the sodium alizarate solution. The solutions were mixed in this proportion and I O O cc of the supernatant liquid was withdrawn and analyzed for sodium; for it was obvious that if the sodium alizarate were adsorbed as the salt, no sodium would remain in the bath. The sodium sulfate was found to be 0.0568 grams. On the basis of equal distribution throughout the mixture, there should have been found 0.0665 grams. Hence more than 8 j percent of the sodium remained in the bath. For the ferric oxide 2 3 7 . 5 cc of the sol was mixed with j o cc of the Y1;ioo sodium alizarate. After mixing the supernatant liquid was analyzed for sodium as in the previous case and 0 . 0 2 53 grams of sodium sulfate was found as compared with 0.0284 grams if none were adsorbed. That is, about 90 percent of the sodium was left in the bath. For the test on alumina lake, a gel was employed instead of a sol. A solution containing about 7 grams of aluminum chloride was precipitated by the gradual addition of ammonium hydroxide. This was washed by decantation with the aid of the centrifuge until peptization was just started. The matted gel occupied about 60 cc. The addition of one cc of the M/IOOsodium alizarate caused nearly complete peptization of the gel. When 5 cc had been added the peptization was complete and the liquid was almost as fluid as water. Cataphoresis experiment on a similar sample showed it to be a negative sol. The addition of more of the sodium alizarate did not have any apparent effect until the total quantity present was 2 5 cc. The viscosity increased greatly from this concentration to a total of about 3 2 cc. More than this started precipitation and when 40 cc had been added, the precipitation was complete. The supernatant liquid was nearly colorless showing that the alizarin was practically all removed in the process. An aliquot part of the supernatant liquid, determined by weight, was analyzed for sodium. I t was found to contain 0.0262 grams of sodium as sulfate compared with 0.0271 grams if none had been adsorbed. This shows that nearly 97 percent of the sodium was left in the bath. If the gel of ferric and chromic oxide had been used it is probable that the amount of sodium remaining in the bath would have been greater than when the highly purified sols were employed. It seems likely that the sodium which is taken up during the precipitation of the sols, is adsorbed as univalent alizarate ions containing one atom of sodium. The pH values of the colorless supernatant liquids showed them to be almost neutral. I t should be mentioned in passing, that the addition of sodium hydroxide to a washed gel of alumina gives results which are not unlike those with sodium alizarate. The gel is first peptized as a negative sol and on the addition of a critical amount of alkali it is reprecipitated giving a supernatant liquid which is nearly neutral and contains most of the sodium. This behavior is what might be expected since both the dye and the base are strongly adsorbed by the hydrous oxides. The question naturally arises, how alizarate and hydroxyl ions could be adsorbed by a Precipitated gel leaving practically all the sodium in the solu-
1830
HARRY B. WEISER A S D EVERETT E. PORTER
tion, without imparting a negative charge to the particles. For this t o happen there must be adsorbed along with the hydroxyl and alizarate a n equivalent quantity of some positive ion other than sodium or there must be liberated an equivalent quantity of some negative ion. The latter is what happens chiefly since it was found that the sodium is associated with chloride which was present in the gel and was replaced by the more strongly adsorbed hydroxyl or alizarate ions. This suggests that a gel from which practically all the chloride was removed would have a very small capacity for adsorbing anions. To test this, hydrous chromic oxide was employed since it is the best adsorbent of the oxides of the iron group. The sol containing 1.42 grams of Cr203 was precipitated with ammonia and washed repeatedly with the aid of the centrifuge keeping the washing very slightly alkaline with ammonia. By this procedure practically all of the chlorine was removed. After washing the gel several times with pure water it was suspended in a little water to which 0.5 cc of the M/IOO sodium alizarate solution was added. After shaking and centrifuging the supernatant liquid was found to be colored showing that there was little or no adsorption of the dye. On comparing this result with the experiment described above in which I O O cc of the same dye solution was exhausted by a like amount of the sol, one sees to what extent the adsorption is dependent on the nature and extent of purification of the gel. I n the last instance the gel was washed with water containing ammonia; the adsorption capacity of the particles was practically saturated with hydroxyl ions, and therefore the gel could take up but little 2f the dye anion. In the first experiment, on the other hand, the conditions were exactly reversed. The sol was peptized by acid and even after prolonged dialysis, the particles were positively charged owing to the preferential adsorption of the hydrogen ion. The sol contains an equivalent amount of the less strongly adsorbed chloride ion, a part of which is adsorbed by the particles and the remainder is present in the intermicellar liquid. On adding sodium alizarate, the strongly adssrbed alizarate and hydroxyl ions not only neutralize the sol by adsorption but displace the adsorbed chloride ion more or less completely. Simultaneous Adsorption of Alizarate and Other Ions The addition of sulfate to the acid baths which give up their color too rapidly has long been followed by the practical dyer. The sulfate by decreasing the adsorption and by retarding the rate of adsorption of the dye anion, tends to give a more even dyeing of the fabric.' S?metinies, however the presence of even a small amount of sulfate is objectionable; this is particularly true in the case of the alizarins. As already noted, Bancroft assumes that the purpose of adding calcium ion as calcium acetate to an alizarin bath is not to give a calcium aluminum alizarate of some sort on the mordanted cloth but to remove sulfate ion, which cuts down the adsorption of alizarin ion. As will be seen in the next section, calcium sulfate is too soluble to enahlp one to account for the action of calcium ion in this way. Bancroft: J. Phys. Chem., 18.
I
(1914).
Pelet-Jolivet1 has demonstrated that readily adsorbed anions such as sulfate and phoephate cut down the adsorption of acid dyes (e.g. crystal ponceau) and readily adsorbed cations such as magnesium increase the adsorption of acid dyes.^ Davison3 made some qualitative observations on the d e c t of sulfatc' ions and of calcium ions on the adsorption of dyes by fibers 3 s well as by alumina. Thus he finds that 8 grams of Sad304 in I O O cc of 113th prevents the dyeing of wool by Crocein Violet. In lower concentrations, rhe dye is taken u p in increasing amounts as the concentration of the sulfntc is ticere *sed. .Ilmnina precipitated from aluminum acetate was found to ad-orb certain acid tiyes, including alizarin, more strongly than that' froiii :duriiinurn sulfate. ('aleiuiii acetate was found to increase the adsorption of rile acid d>.c ('rocein Orange but to decrease the adsorption of the acid dyr .kcid (;reen, 'I-hcre art' other inconsistencirs such as one might expect in clualitative ohsrrvatims. In the suhvquent paragraphs are given thr resultsof quanritative obsermtions on t h e effecr of both sulfate ion anti of calcium ion on the adsorption of :rlizarins by iiiordants at varying hyc1rog.cn ion conccntration:;. The observation> show clcarly the action of neutral salts on color lakc forniation. Thc Elfeet oj S / I / j f i f P the .4O,wrpfzo~/ii,f .4/izi/rin S1T7. .1 series of ob-crvarions was niade t c tleteriiiine the effect of ~ u l f a t eon the adsorption of dizarin SJJ- by hyilrous cliroiiiic oxide at varying pH values. The method of ~ ~ r o c c t l u TWS r e e ~ s c n t i u l lt ~ h c~ same as was used in determining the effect of *ulfate on thc :idsori)tion ~ ioxalate ' in an ear1ic.r paper.; 'I'ht, data are suiii~iiarizrtlin Table I\. m t l plotted in Fig. 2 . Just as i n t h i l e \vi11 hc noted that thc Ifatc. ha.3 little effect on thc, aclwrptitr :inion in thc neutral d hasic solutions since, ~intlcrt l i c w c.ontfitions. t l i r . presence of thc much i i i o r ~strongly adsorbed hytlros~-li o r l ~iiacksthe relatively smail effect of thv d f n t c . In the acid range, h(J\Yt'TPr, the effrct of sulfate is quite inarkcd. Pincc the dye anion is iltlwrhetl iiiore strongly thaii iulfate from the same concentration, one niiyht expect the latrer to 1ial.i. little effect in the adsorption of the forrnrr. But the hrhnvior of the tlycs isimilar to that of thc oxalate. In the acid solution the cffc,ctivt concentration of the dye becoiiirs T small due to the Fuppressing of thc ionization, an(l the action of sulfate iiianifmts itself. If the sulfate had 1m.n determinctl in tl heon siriiilar throughout t o the series of expcrinients the results ~ v v o i ~ lhave those ohtaincd with sulfirtr and osnlato; viz. sulfate adsoi,bd more from tlic acid and d y e adwrbcd I I I O ~ C from the neutral and basic bath. Sincc acitl baths are usually eniployc~~ in dyeing acid dyes, thc rctartling effect of sulfate' is explained even though the dye cation may he 1 1 1 0 1 ~qtrongly adsorbed than sulfate ion from thr sanir' concentration. I
: "Die Theorie des Fiirheprozesses," 94, 98. I 1 9 , 118 ' 1910 ?Bancroft: .J. Phys. C'hern.. 18, I I 1191.i). J . Phys. C h e m . , 17, 73; ' 1 9 1 3 , . * .J. Phys. (.'hem. 31, 0000 ( 1 9 2 7 ) .
1832
HARRY B. WEISER AND EVERETT E . PORTER
TABLE IT' Adsorption of Alizarin SW at varying pH Values in varying Concentrations of Sulfate Ion Cc of aoln. mixed with I O cc of sol containing 0.012 gram of CrzOsin a total oJ35 cc. 0.0
H&
y
0.02
ix
HzSOI
s
0.02
KzS01
,0.037
Adsorption value in millimoles alizarin SW per gram CrtO3
KOH
0.003 hl dye
1.64 I .63
5
0
0
0
IO
2
0
0
0
IO
0
0
0
0
IO
1.52
0
0
0
I
IO
0.77
3
0
0
2
IO
0.06
0
2
0
0
IO
1.30
0
0
2
0
IO
5
5
0
0
IO
1.39 0.84 0.89
0
5
0
0
IO
0
2
0
IO
1.02
0
0
3 5
0
IO
1.31
0
0
5
2
IO
0.25
0
IO
0
0
10
0
5
5 8
0
IO
0.33 0.39 0.74
pH of mixture
2'507
2.800 4.212 8.321 9.174 2.870 5.000
2.416 2.586 2.998 4.907 8.887 2.361 2.699 3.280
0
2
0
IO
0
0
IO
0
IO
1.27
5.512
0
0
IO
2
IO
9.161 2.484 2.876 3.431 3.815 6.012 8.817
0
IO
IO
0
IO
0.29 0.08
0
5
0
IO
0.14
0
2
0
IO
0
I
'5 I8 '9
0
1 0
0.49 0.85
0
0
20
0
IO
1.22
0
0
I8
2
IO
0.33
PHTSI CAL CHEMISTRY OF COLOR LAKE FORMATION
7833
The Effect of Calcium Ion on the Adsorption of Alizarin SW. The results of the observations on the adsorption of alizarin SW in the presence of varying amounts of calcium ion as well as varying hydrogen ion concentrations are given in Table T' and plotted in Fig. 3. Just as the effect of sulfate ion is TABLE
v
Adsorption of Alizarin SW a t varying pH Values in varying Concentrations of Calcium Ion Cc of s o h . mixed with 5 cc of sol containing 0.0125 gram of C r 2 0 3in a total of 35 cc. 0.0
s
H&l
0.013 Y
cah,
Adsorption value in millimoles alizarin SW per gram Cr?Oa
0.037 S KOH
0.006 AI
dye
.62
2
0
0
I
0
0
0
0
0
0
0
I
5 5 5 5
0
0
2
5
2
2
0
0
2
0
0
2
I
5 5 5
0
2
2
5
0
2
4
2
4 4
0
5 5
0
5
I
0
5 5 5 5
.63 1.57 1.59 1.35 0,30 I ,63
0
5
I.
I
5 5
1.62 I .61 0.91 1.63 1.61 1.65 I .63 I .63
0
0
4 4 4 6 6 6 6 6
I
IO
0
0
IO
0
0
IO
I
0
IO
2
0
IO
4
0 0 0
I 0
0 0
2
4
2
4
P.H of
mixture
5 5 5
5 5 5
I
I.
j8
I .52
0.77 0.06 I .62 1.54 1.46 0.83 0.20
I
58
2.606 3.000 4.212 8.321 9 . 174 3 , '03 4.904 8,206 8.924 10,311 3.010 4.490 5,892 9.041 10.379 3.100 4.239 8.j 1 2 8.683 10.031 3.091 4.247 s I52 8.248 9.049
small in the presence of the relatively highly adsorbed hydroxyl ion, so the effect of calcium is small in the presence of the relatively strongly adsorbed hydrogen ion. The effectiveness of the calcium increases with its concentration and with the concentration of the base until the solution becomes sufficiently basic to overbalance the calcidm ion effect. From this one would expect the presence of a strongly adsorbed cation such as calcium to be particularly effective in the application of dyes that are insoluble in the acid bath. This
HARRY B. WEISER AND EVERETT E. PORTER
I834
is the function of the calcium in dyeing with alizarin. Thus, in the presence of calcium one may use a slightly basic bath in which the alizarin is soluble and at the same time increase the adsorption of the dye anion so that it is not replaced by the hydroxyl. All of the data of Tables IT' and T' were plotted adsorption against pH and the increase in adsorption due to calcium, as well as the decrease due to the sulfate read off at constant pH values. The resulting data are tabulated
TABLE VI The Effect of varying the Concentration of Salts on the Adsorption of Dye at Constant pH The effect of potassium sulfate
The effect of calcium chloride Increase in CaC12 Adsorption a t
N conc.
PH
=
9
pH =
S conc.
pH=3
j
0.0008
0 .jo
0.0;
0.0011
0.0016
I.
17 1.37 1.51
0.06j 0.099 0.129
0.0029 0.0057
0.0024
0.0040
Increase in Adsorption a t
K*SO,
0.0114
p H = j
0.29 0.81
0 .I2
.oj
0.23 0.29
I
1.37
0.18
as Table VI and shown in Fig. 4. The reason for taking these values from a graph is that it was not possible to make a series of mixtures that would all come to exactly the same equilibrium concentration of hydrogen ion. The reading off of values from the curves seemed to be the best method of interpolation. It will be noted that the effectiveness of the calcium approaches zero as the pH value decreases while that of sulfate increases with decreasing p H value. T h e Effect of Calcium Sulfate o n the Adsorption of Alizarin SW at i'arying Hydrogen ion Concentrations. Since the foregoing experiments show that the effect of the sulfate is large in the acid and negligible in the basic baths and
PHTSICAL CHEMISTRY O F COLOR LAKE FORXATIOK
I835
that the effectiveness of the calciuni increases with the hydroxyl ion concentration, one is lead to conclude that if calcium sulfate were present the effect of the sulfate would predominate in the acid solutions and that the influence of the calcium would be unaffected by the sulfate in the basic baths. Direct experimental verification of this conclusion is given by the data recorded in Table VI1 and plotted in Fig. j . If Figs. 2 , 3, and j, all of which are plotted
TABLE TTI Adsorption of Alizarin SJV at varying pH I-alues in varying Concentrations of Calcium Sulfate Adsorption value in millimoles alizarin SU' per gram G O 3
Cc of soln. mixed with 5 cc of sol containing 0.0125 gram of Crz03in a total of 1 5 cc ~
pH of mixture
~~~
0.04 S
HC1
o.ozi4 S
CaSOr
0.037 S
KOH
0.006 11
dye
2
0
0
1.62
2.606
I
0
0
I.j8
3.000
0
0
0
I.j2
4.212
0
0
I
0,:;
8.321
0
0
2
0.06
9.114
1
I
0
I
2,207
I
0
,43 I ,40
I
I
0
I
0
I
0
1.44
0
I
2
0.j 8
38
2,606 3.002
j.158 8.611
10.441
0
I
>
0.03
,
2
0
I .13
2.129
1
0
I ,09
2.522
1
7
0
1.19
2.825
0
2
2
1.40
8.619 10.385
0
2
5
3
0
0.26 0.92
0
0.80
2.494
0
1.00
2.803
0
3 3 3 3 3 3
>
5 1
0
0
2 I
2.1j4
0
1.39
5.967
2
1.;:
8.202
>
0.41
0
0 .j6
2.146
0
0.6j
2,501
>
0
1.47
5.122
2
2
5 5 '5 '5
0
15
0
I.j3
0
I5 15
2
1.6j
8.386 0.815 2.396 2.93' 4.176 8.jj1
5
1.6j
8.80j
0 0
0
>
0
5
1.61 1.62
0
0 . 2 j
0
0,20
I O .2 8 0
1836
HARRY B. WEISER AND EVERETT E. PORTER
on the same scale, are superimposed so that the adsorption curves in the absence of any salt coincide, 5 and 2 are alike in the acid range while 5 and 3 are alike in the basic range. These data show that the effects of the calcium and sulfate ions in the bath are practically independent of each other and that each is dependent on the hydrogen ion concentration.
PHYSICAL CHEhlISTRP O F COLOR LAKE FORYATIOS
1837
T h e Effect of Calcium I o n and of Sulfate I o n on the Adsorption of Alizarin. Observations on the effect of calcium and sulfate ions on the adsorption of alizaratz ion from a sodium alizarate bathare giveninTable VI11 and plotted in Fig. 6. Since the bath must be basic in order for the dye to remain in solution. ThBLE
VI11
The Adsorption of Alizarin a t different Calcium, Sulfate, and Hydroxyl Ion Concentrations Cc of soln. mixed with 5cc of sol containing 0.0125 gram of C r 2 0 rin a total of 35 cc. 0.0
s
0.02
s
HC4
li2SOI
0.037 S
IiOH
Adsorption value in millimoles alizarin per gram CrlOB 0.003
o,;;&i2S
JI Alizarin
I .o
0.0
0.0
IO
0.0
0.5
0.0
0.0
IO
0.0
1.19
0.2
0.0
0.0
IO
0.0
I.jj
0.0
0.0
0.0
IO
0.0
0.64 0.39
0.0
0.0
1.0
IO
0.0
0.22
0.0
0.0
2.0
IO
0 0
0.13
1.0
I0
0.0
IO
0.0
1.43
0.5
IO
0.3
IO
0.0
1.11
0.2
IO
0.0
IO
0.0
0.69
0.0
IO
0.0
IO
0.0
0.41
0.0
IO
I .o
IO
0.0
0.23
0 .j
0.0
0.0
IO
2 . 0
1
0.2
0.0
0.0
IO
2.0
1.42
0.0
0.0
0.0
IO
2.0
1 . so
0.0
0.0
I .o
IO
2.0
1.25
53
0.0
0.0
2.0
IO
2.0
I , 13
I .o
0.0
0.0
IO
5.0
I .62
0.5
0.0
0.0
IO
5.0
1 ,51
0 . 2
0.0
0.0
IO
5.0
1.5'
0.0
0.0
0.0
IO
1.5.;
0.0
0.0
I .o
IO
5.0 5.0
0.0
0.0
2.0
IO
5.0
I
0.0
0.0
5.0
10
j.0
1.62
I .60
.62
one would expect the effect of sulfate to be slight, as the observations show. On the other hand, the effect of calcium is marked and increases with its concentration. Hence by the addition of a strongly adsorbed cation one may use a slightly basic bath in which the alizarin is soluble and at the same time avoid the displacement of the dye anion by the hydroxyl. This is the functior, of
1838
H.IRKY B. \TEIbER . I S D EVERETT E . PORTER
the calcium ion in the formation of alizarin lakes. That the effectiveness of the calcium is not due t o the direct precipitation of calcium alizarate is evidenced by the fact that the quantity of calcium present may be grcater than the equiralent of the alizarin without the dye bath becoming exhausted
I
SN
OH Summary I.
X study has been made of the mcchnnisrn of the formation of alizarin
lakes with the hydrous oxides of iron, chron:ium and aluminum and the influence of the concentration of the hydrogen ion and other ions on the lake formation process. 2. In every case lake forniation is due to the adsorption of the dye anion by the hydrous oxides in varying amounts depending on the composition of the dye bath. 3 . The influence of h3-drogen ion concentration on the adsorption of alizarin S K is similar to that on sulfate and on oxalate. The order of adsorbabilities from the neutral and basic baths is alizarin S K >oxalate >sulfate. 4. The formation of alizarin lakes from sodium alizarate baths is due to adsorption of the dye anion by the hydrous oxide and not to the direct ndsorption of the neutral sodium alizarate sssuggested by Bull andhdams and by Tilliamson, or to double decomposition betffeen the dye and the oxide as proposed by Biltz in the case of ferric oside. 5 . The effect of sulfate ion on the adsorption of alizarin S W is similar to its effect on the adsorption of oxalate, sulfate replacing the dye if the bath is acid. The power of the sulfate ion to replace the dye anion decreases to zero as the bath becomes alkaline. 6. The effect of calcium ion on the formation of alizarin lakes is to increase the charge on the mordant, thereby enabling it to adsorb more of the dye anion rathcr than t o remove sulfate from the bath as suggested by I 3 m croft, or to form n eompl~xcalcium aluminum alizarate.
PHYSICAL CHEMISTRY O F COLOR LAKE FORJIATIOS
1839
7 . The salt effects in the niordanting processes may be summarized as follows : ‘a1 The presence of a strongly adsorbed cation in the dye bath increaseq the rate and quantity of adsorption of acid dyes and has an opposite effect on basic dyes, its effect increasing with the pH of the bath and with its own concentration. 1 b) The presence of a strongly adsorbed anion in the dye bath decreaseq the rate and quantity of adsorption of acid dyes and increases the adsorption of baeic dyes, its effectiveness increasing n-ith the acidity of the solution and with its own concentration. ( c ) If the dye bath is either acid or basic the effects of the cations and anions are practically independent of each other, the influence of the cation predominating in the basic bath and of the anion in the acid baths. The abore conclusions apply also to the dyeing of fibers in the absence of :i iiiordant . l l i t Rice Inqtitvte. Iiov.fon, Yrrob
