January, 1924
INDUSTRIAL AATDENGINEERING CHEMISTRY
35
T h e Influence of Variation in Concentration on t h e Absorption Spectra of D y e Preliminary Paper By Walter C. Holmes COLORLABORATORY, BUFdAU OF CHEMISTRY, WASHINGTOX, D. C.
F
A summary is given of a preziminary study of the variation in million Parts of solvent) it absorption of over one hundred dyes resulting from the variation of as necessary to construct (:randmougin4 have the Concentration of their aqueous solutions ouer a wide range. suitable very thin cells.10 supplied a summary Early in the course of the of concentration effects obI n the instance of a considerable number of dyes a radical type of modificafion in absorption was established, which is interpreted measurements it became served in their SPectroscoPic apparent that fern7, if anyt examin:hon of S~veralthou- as evidence that the dyes in question are present in aqueous solution in a state of tautomerism between two constitutional forms, with the dyes conform Precisely to sand dyes with a technic inTTolviW a systematic equilibrium depending upon the concentration of the solution. Beer’s law11 over any extensive range in concentravariation in concentration over a moderate range and tion. Apart from symwith methods which were quantitative only in respect to the metrical modifications of the absorption bands, accompanydetermination of the locations of absorption maxima. They ing minor deviation from Beer’s law, displacements of the state that the relative intensities of the two bands of the maxima and appreciable unsymmetrical modifications in the spectra of diarninotolazthionium and diaminonaphthazoxon- essential form of the absorption curves were frequently obium derivatives are altered. Further reference is made to a served, which were, in numerous instances, of a radical order. number of individual dyes which undergo various minor With the recognition of these latter phenomena which prechanges in the positions and relative intensities of their bands, vious investigation has given but slight reason to anticipate, occurriiig within comparatively brief periods after the prep- the more immediate object of the investigation became that of aration of their solutions (by dilution) and constituting, the examination of as comprehensive a selection of dyes as was apparently, dilution effects requiring an appreciable period of possible in order t o determine how general their occurrence time for completion. Alizarin Green G and B (D) are cited might be and to obtain such evidence respecting their cause as examples of dyes with which this alteration is of consider- as was possible in a study of a preliminary character. able proportions and as being the only dyes with which The work has included the measurement of the absorptions essentially radical alterations in spectra were observed. in the visible spectrum of more than five hundred ‘aqueous Quantitative investigation in this field has been too in- solutions, employing over one hundred different color types. complete in scope to afford any adequate basis for conclusions I n the instance of various color types a number of dyes of respecting the effects of wide variations in concentration different manufacture have been examined. upon the essential aspects of the absorption of dyes in general. It is expected that arrangements may be made eventually The daia which have been supplied in the instance of seven for the publication of the majority of the more significant of permitted food dyes6 were not intended, and are not well the absorption curves obtained, together with other curves adapted, for that specific purpose. Those supplied by Shep- of interest in different connections, in the form of an atlas. pard6 are of interest but are decidedly meager. In the study In the present communication it is necessary to resort prinof concentration effects made by Kalandek’ with solutions cipally to a tabular presentation of a minimum quantity of of nine dyes the range in dilution employed was small. The data, which can only serve to define somewhat roughly that value of the numerous earlier investigations in the field, which aspect of the phenomena observed which is of chief interest. have been reviewed and discussed by both Rudorf8 and RESULTS K a y ~ e r was , ~ seriously impaired by the general failure t o ‘ In the accompanying tables and lists only one example of recognize the necessity of carrying out the absorption measureeach color type has been included. (In several instances two ments over an extended spectral range. dyes with the same Schultz number have been listed when EXPERIMENTAL it has been apparent that their constitutions must necessarily In the)present investigation 3, Hilger %rave length spectrom- be decidedly divergent .) The recorded absorption maxima eter eqrlipped with a xutting photometer was employed. were usually determined with only moderate precision. The For the examination of relatively concentrated solutions (con- concentrations at which the measurements were made are taining from five hundred to several thousand parts of dye per expressed in terms of Parts of dye Per million Parts of solventUnless otherwise specified the solvent employed was distilled
O R M A N E K and
1 Precsented before the Division of Dye Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922, and revised with the inclusion of additional data, Received February 2, 1923 * Contribution No. 71 from the Color Laboratory, Bureau of Chemistry. a The investigation was begun and the earlier measurements were made a t the Technical Laboratory of E. I. duPont d e Nemours & Company. 4 “Untersuchung und Nachweis organischer Farbstoffe auf Spektroskipischem Wege,” Erste Teil. Berlin, 1908. 6 Bur. Standards, Sci. Paper 440. 8 Proc. Royal SOC.(London), 82A, 256 (1909). 7 Physik. 2 , 9, 128 (1908). 8 Ahren’s Samml , 9 (1904), Jahrb. Elektronik, 3, 423 (1907). 0 “Handbuch der Spectroscopie,” 3, 109 (1905).
water. In the instance Of a large majority Of the dyes examined the dilution of their solutions over the range employed resulted in appreciable displacements of their absorption maxdegree of unsymmetrical modification ima, together with form Of their absorption curves* in the Pontachrome Violet S W and Diamine Black B 0 afford exceptions to the general rule that the direction of the shift 10 11
11
THIS JOURNAL, 15, 833 (1923). P o g g . Ann., 86, 78 (1852). Color Trade J., 13, 54 (1923).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
36 TABLE I-Azo DYE Pontacyl Carmine 6 B (duPont). Bordeaux B (Ber.) Methyl Orange (Basel) Azo Fuchsine G N Extra (By.). Pontacyl Fast Red A S (duPont). Pontacyl Ruby G (duPont) Pontacyl Sulfon Violet R (duPont).. Buffalo Black N B R Concentrated (Nat.) Pontacyl Sulfon Blue 5 R Concentrated (duPont) Pontamine Fast Pink B L (duPont) Congo Red (duPont). Erie Garnet B (Nat.). Heliotrope 2 B (By.).. Pontamine Violet N (duPont).. Erie Violet 3 R (dissolved hot)o (Nat.) Erie Violet 3 R (dissolved cold)o (Nat.) Erie Red 4 B (Nat.).. Vital Red (laboratory). Benzo Blue B X (By.) Diamine Blue Black (dissolved Cold)5 (e.).. Diamine Black B 0 (dissolved hot)o
DYES Maximum Maximum in in Dilute Concentrated Solution Solution ,u,uP.p.m. ~ , u P . p . m . 525 100 514 2000 515 82 510 2000 465 1 465 250, 520 50 515 1000 505 40 500 1000 512 2 505 2000 550 2 530 4000
Schultz No.
.... ................. .............. ...... ....
66 112 138 147 161 163 185
........... ......................... 217 .............. 257 . . 297 ............. 307 ............. 312 ............. ..... 321 327 ......................... 327 327 ......................... 363 ............. ............ 370 .............. 386
40
600
1000
565 520 495 520 545 525
2 4 2 50 80 40
550 515 485 520 545 520
2600 4000 2000 1000 2000 1000
525
80
520
2000 2000
{Elso
................... 402(?)
........................... Diamine Black B 0 (dissolved
403
(C.)
620
498 500 560
2.5 2.5 100
{ 490 %j 500 560
1000 1000 2460
580f
80
580-
2000
570
80
580
2000
(c.).....................
403 580 80 600 2000 cold)5 603 2 595 426 Pontamine Sky Blue 5 B X (duPont) 2000 474 2000 Pontamine Green B X . 620 80 620 Pontamine CouDer Blue R R X 555 2 545 (duPont). 1 4000 515 2 548 PQntachrome Violet S W (duPont) 2000 2000 Diazo Dark Blue 3 B (By.).. . . . . . . . 570 80 560 Diazine Black D R Concentrated 565 100 560 2000 (Nat.) 575 2 555 Pontachrome Green G L 0 (duPont).. 2000 o The significance of the modification in the absorption of these and of certain other dyes with variation in the temperature at which their aqueous solution is effected has been discussed elsewhere.12
............. ..... ................. ... ... ... ... ......................... ... ...
of the maxima with increasing dilution is toward the red end of the spectrum. The alterations in the absorption of the azo dyes in general upon dilution are less considerable in degree than is the case with dyes of various other classes, and have received less study. Comparatively few measurements were made a t concentrations which were intermediate between those recorded.
Vol. 16, No. 1
Both the relatively stable and the unstable groups of these dyes include examples of both basic and acid character and of both symmetrical and unsymmetrical constitution. Since the absorptions of Para Rosaniline, Fuchsin, New Fuchsin, and Acid Magenta are relatively stable to change in concentration, it appears evident that the susceptibility of the dyes of this group to radical modification in absorption upon dilution is dependent upon substitution within the amino groups. It is of interest to observe that stability is restored through the conversion of Methyl Violet or Crystal Violet into Methyl Green, with the attendant alteration in nitrogen valency. Attention may also be directed to an apparent relationship in the data, which appears significant. The basic dyes, Hoffmann Violet, Methyl Violet, Crystal Violet, and Ethyl Violet, and the acid dyes, Pontacyl Violet C 4 B and Alkali Violet R, are derived from Fuchsin exclusively through substitution within the amino groups. Although the absorptions of these dyes in dilute solutions are individual, distinctive, and widely different from that of Fuchsin, their absorptions in conceptrated solutions are all approximately identical with that of the latter dye. I n other words, the effects of the substitutions are lost, so far as concerns light absorption, in passing from dilute to concentrated aqueous solution. Numerous measurements carried out upon solutions of concentrations intermediate between those recorded leave no doubt respecting the essential character of the phenomenon with various dyes of this group. It is not one of a gradual shifting in the location of an absorption band, but rather one of a transition between two bands which have definite locations in widely separated portions of the spectrum and which may be observed in progressive degrees of ascendency. Their relative intensities are dependent upon concentration. By means of suitable variation in the latter respect either band may be developed a t the expense of the other.
TABLE 11-TRIAMINO DERIVATIVES OF TRIPHENYLMETHANE AND DIPHENYLNAPHTHYLMETHANE
DYE Para Rosaniline (pure dye) Fuchsine B Cr stals (Nat.) New Fuchsin 1,. B.) HoffmanqViolet B.) Methyl Violet N (duPont) Crystal Violet E (duPont).. Ethyl Violet (B.) Methyl Green Crystals I Yellow Shade (By.) Victoria Blue 4 R (B.) F a s t Green Extra (By.) Fast Green C R (By.) Acid Magenta (Sch.) Redviolet 5 R S (B.)
Schultz No. 511 512 513 514 515 516 518
.........
......... &. ............... ........... 4 ........ ........
.................. .......................... ............. 519 522
............ 623 ............. ............... 523 524 ..............
525
................. 527 527 .............. ..... 530 .......(Note 530 3) Alkaliviolet R (By.) .............. 532 Methylalkaliblue (M. L. B.).. ...... Alkali Blue 6 B (By.).. ............ 585 Bavarian Blue D S F (B. ?). ....... 537 (?) Soluble Blue (duPont) ............. Pontacyl Violet 6 B N (duPont) .... 548 Victoria Blue R (duPont). ......... 558 Victoria Blue B (duPont) .......... 559 Pontacyl Blue R (duPont) .......... Acid Violet 4 B Acid Violet 6 B Pontacyl Violet Acid Violet 4 B
N
(By.) C 4 B (duPont) Extra (BY.).
.............. ...............
Night Blue (Griibler) Intensive Blue (By.)
560 562
Maximum Maximum in in Diluted Concentrated Solution Solution p,uP.p.m.pp P,p.m. 539 10 539 250 541 10 540 250 544 10 541 250 585 0.5 540 500 580 25 540 1000 590 1 540 500 595 10 540 250 635 590 622 630 545 550
40 40 60 60 2
100
590 570 590 575
6 4
590 590 580 595 560 620
2 3 2 5
1 1.6
1 100
635 545
1000 1000 3000 630 3000 545 1000 General absorption at high concentration 550 3000 535 2000 540 2000 530 1000
{ti:,]
540 585 590 580 555 54p,,to
.
1000 60 4000 1000 1000 2000
OYU
605 615 620 620 615
3.8 1.3 2
1 2
565 665 575 570 613
500 500 4000 1000 1000
The absorptions of the majority of the triamino derivatives of triphenylmethane and dipbenylnaphthylmethane are affected in a decided degree by change in concentration. The only exception noted to the general rule in respect to the direction of the shift upon dilution was that of Alkali Blue 6 B.
WAVE LENGTH 1 2
3
--
3
FIG.I-PINACHROME(HI 230 parts per million of 0 1N NaOH solution 9.2 parts per million of 0.1 N NaOH solution 0.74 part per million of 0.1 N NaOH solution
4 = 230 parts per million of 95 per cent alcohol
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1924
The diamino derivatives of triphenylmethane and diphenylnaphthylmethane which have been examined are listed below, together with the range in concentration employed.
37
The nature of the solvent has been shown to exert a decided influence upon the phenomena under investigation.
P. p. m. 10 t o 800 40 t o 1000 2 t o 4000 2 t o 4000 40 t o 1000 20 t o 500 40 to 1000 40 t o 5000 20 t o 500 40 t o 1000 40 t o 1000 40 t o 1000 40 t o 1000 40 t o 1000 1 t o 1000
Schultz No. DYE 495 ViFtoria Green W B Crystals (Nat.).. Brilliant Green B (B.). 499 502 Pontacyl Green B (duPont). 505 Pontacyl Light Green S F Yellowish (duPont) .. 506 Alphazurine F G (Mat.). .. 507 Xylene Blue V S ( S . ) . X d e n e Blue A S IS.). ........................ 508 Afphazurine A (Nat.’) ......................... 5’43 Neptune Blue B G (B.). ...................... Patent Blue A (M. L. B.), 545 Alphazurine 2 G (Nat.).. ..................... Cyanole Extra (C.).. ......................... g46 New Patent Blue B (B ) . . . . . . . . . . . . . . . . . . . 563 New Patent Blue 4 B &y;j 563 Pontacyl Green S N Extra (duPont).. .......... 566
........ .. ................ .. ... .................... ...................... .....................
....................
....................
i
i l l / i
i
i
l
No appreciable alterations were observed in the locations of the absorption maxima of these dyes except for a small displacement in the instance of Brilliant Green B. With increasing concentration, however, their absorption curves underwent a comparatively small, progressive, unsymmetrical modification, which was plainly indicative of the incipient development of new bands in a position considerably nearer the violet end of the spectrum. The a,bsorptions of Fluorescein, both in the form of the color acid and of the alkali salts, and those of the alkali salts of’ I pure tetrachlor-, tetrabrom-, and tetraiodofluorescein, in ’480 500 520 540 560 580 600 620 which the halogen substitution was erected in the phthalic WAVE LENGTH anhydride residue of the molecule, were found to be decidedly FIG.11-CRYSTAL VIOLET modified by change in concentration. On the other hand, 1 1 part dye per million parts water 4 dye base in alcohol solutions of commercial samples of Schultz h’umbers 587 to 2 = 500 parts dye per million parts water 5 dye base in acetone 597, as well as of the alkali salts of dibrom- and octaiodo3 = dry dye per million parts water 6 = dye base in benzene fluorescein and of pure tetrabrom- and tetraiodoeosin, were found t o be entirely stable. It is evident that halogen subThe following dyes have been investigated in solution in stitution within the resorcin residues of Fluorescein renders 95 per cent alcohol over the range in concentration recorded. the absorption of the product stable to change in concentraP. p. m. tion, whereas substitution within the phthalic anhydride Acid Magenta (Sch.) ......................... 8 to 330 Crystal Violet E (duPont).. . . . . . . . . . . . . . . . . . . 10 to 500 residue does not have that effect.13 Crystal Violet Base (duPont). . . . . . . . . . . . . . . . . 10 to 500
--
-
TABLE 111-OXAZINE, THIAZINE, AND AZINE DYES
Maximum in Dilute Schultz Solution DYE No. up P . p . m . Gallocyanine W (duPont) 626 620a Meldola’s Blue (B.) 649 575 2 Nile Blue A (B.). 653 635 8 Nile Blue 2 B (B.) 654 650 1 Lauth’s Violet (Laboratory). 595 Methylene Blue B (duPont) 659 663 1.3 Methylene Green (B.). 660 640f 40 663 630 1 New Methylene Blue N ((2.). Toluidine Blue 0 (B.) ........... (Green 654) 635 1 Safranine B Extra B ).. . . . (Green 583) 520 20 Safranine T Extra [duPont): 679 515 2.5 Rhoduline Red B (By.). . . . . . . . . 684 533 40 Rhoduline Blue R (By.).. ... 565 80 a T h e curves obtained were very broad and indefinite.
...
....... ............. .............. .............. .... ..... .........
...
...
....
::
.......
Maximum in Concentrated Solution ppP.p.m. 5200 550 1000 580 665 592 825 555 600 300 605 1000 575 500 580 1000 515 500 495 1000 510 1000 550 2000
...
All the oxazine, thiazine, and azine derivatives examined gave appreciable dilution effects. With the majority of oxazine and thiazine dyes the curves obtained define clearly a transition between two definite and widely separated absorption bands. TABLE IV-MISCELLANEOUSDYES DYE
Rhodamine 6 G (duPont)
.....
Rhodamine B Extra (duPont)
.
.......
Violamine B (duPont). Violamine 2 R (duPont) . . . . . . Patent Phosphine (Laboratory) Pinachromeo M. L. B.) Orthachrome &a (M. L. B . ) . 1-Naphthol-2-sodium sulfonate indophenol (pure dye). Indigotine Conc. (duPont) ..... Alizarin Blue S 5 R (By.). a Made up with 0.1 N NaOH.
Schultz No. 571 573 580
....
. . . . .. .. . ..606 ... ........
-
. . . . .877 ..
Maximum in Dilute Solution &a P.p.rn. 525 553
0.6 la3
545 525 472 575 570
2 2 40
500 610 560
75 2 40
0.7
1.2
Maximum in Concentrated Solution uu P . P . ~ .
I:;]
1000
535 525 470 530 520
500 2000 2000 1000 230 722
500 610 540
2500 4000 1000
I* The: writer is indebted to the D. S. P r a t t Fellowship, Mellon Institute of Industrial Research, for the pure halogenated derivatives of Fluorescein examined.
Erie Red 4 B (Nat.).. ....................... Fluorescein-color acid.. ..................... Fluorescein-sodium salt.. . . . . . . . . . . . . . . . . . . . Methylene Blue B (duPont) .................. Orthachrome T (M. L. B.). . . . . . . . . . . . . . . . . . . Pinachrome (M. I,. B.) Pontacyl Green S N Extra (duPont).. Rhodamine B Extra (duPont). Rhodamine B Base (duPont). Corallin(Grtib1er).
....................... ......... ............... ................
...........................
50 to 2 . 5 to 2 to 1.3 to 2.5 to 0.5 to 1 to 10 to 10 to 43 to
1000 250
250 125 230 230 1000 500 1000
1000
The absorption maximum of the solution of Corallin underwent displacement from 460 p p to 480 pp upon dilution. An appreciable modification was also observed in the absorption of the solution of the alkali salt of Fluorescein, although it does not appear certain that the alteration was necessarily a dilution effect in that instance. No decided modifications of any character were observed, however, in the absorptions of the other dyes listed, and it may be concluded that the alcoholic solutions of dyes in general are essentially stable to variation in concentration. The absorptions of the color bases of Crystal Violet and Rhodamine B in alcohol were found to be practically identical with those of*the corresponding dyes in alcohol and to differ from those of the dyes in dilute aqueous solutions only in very minor respects. An analogous relationship was established in the instances of other dye bases. In benzene, however, the dye bases develop new bands which are radically different from the bands of either dilute or concentrated aqueous solutions of the dyes. The absorptions of a number of these same basic dyes have also been measured in the “dry” condition by drying their solutions on microscope slides, employing gelatin with solutions which do not otherwise give satisfactory films. Absorption curves have been obtained in this manner which have shown a close correspondence in position with the curves of concentrated aqueous solutions of the same dyes.
,
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
38
The behavior of Crystal Violet may be accepted as typical of that of various other basic dyes. The dye base in benzene gives an absorption band with a maximum a t approximately 490 p p , the “dry” dye a second band with a maximum a t 1.5 1.4 1.3 g 1.2 1.1 i; 1.0 LL g .9
g
.8 J
= 3
F:
.6 .5 .4
3
480 500 520 540
560 S O WAVE LENGTH
600
620
640 660
FIG.111-VICTORIAB L V E B 1 = 1.28 parts per million 3 = color base in alcohol 2 = 500 parts per million 4 = color base in benzene
about 540 ,up, and the dye or the dye base in alcohol (or the dye base in acetone) a third band with a maximum near 590 p p . These three absorption forms are well defined and widely divergent. Aqueous solutions of the dye exhibit an equilibrium between two absorption forms which are clearly essentially identical with the second and third forms enumerated. It will be well to precede any discussion of the significance of the results obtained to date in this investigation by a consideration of the possible interference of several factors. INTERFERING FACTORS A limited degree of variation in the hydrogen-ion concentration of aqueous solutions employed in comparative examinations may have exerted some minor influence upon the results obtained with some of the dyes employed. An effect of this character was noted in the examinations of Fluorescein, and the instability of the absorptions of Fluorescein and of pure tetrabromfluorescein (substituted in the phthalic anhydride residue) to the variation of their concentration in solution in distilled water was verified by corresponding examinations in buffered solutions. It may be noted, however, that very few of the dyes employed are appreciably affected by any such range in hydrogen-ion Concentration as could have been encountered in their investigation, and, furthermore, that the absorption equilibria which are dependent upon hydrogen-ion concentration are, in general, of a radically different character from those dependent upon concentration. The bands which are found with concentrated solutions of such dyes as Crystal Violet or Methylene Blue cannot be developed in dilute solutions of those dyes with either acids or alkalies. Although it was considered decidedly improbable that variation in temperature would exert any appreciable influence upon the absorption equilibria in question, the absorptions of solutions of Methylene Blue were measured a t 20” C., 80 O C., and several intermediate temperatures. No alterations could be detected in the form of the absorntion curves over the entire range in temperature employed. The materials employed in the investigation have been of varying degrees of purity. No examples of color types have been listed which were plainly deliberate mixtures or in which it was possible to detect the addition of added dyes for shad-
Vol. 16, No. 1
ing purposes in other than very small quantities. The character of numerous commercial products examined, however, was doubtless decidedly heterogeneous. On the other hand, some of the commercial samples were relatively free from subsidiary coloring matters, while other sampIes of laboratory origin or purification were unquestionably of excellent purity. In considering the possible interference arising from the presence of subsidiary dyes, it should be borne in mind that the absorption of such dyes in general will resemble somewhat closely that of the principal color type and undergo modification along the same general lines. Although color impurities may be expected to obscure in some degree the exact quantitative definition of an absorption equilibrium, they would not be expected to modify the essential character of the phenomenon. Even the quantitative relation may remain practically unaffected. With a considerable number of commercial samples of dyes of the Patent Blue type only slight variations were observed by the writer in the values of a spectrophotometric ratio which recorded a quantitative measure of a concentration effect.14 It was shown that the ratio in question afforded a reliable means of differentiation between two types of amino substitution. , I n the present study a large number of commercial samples of Crystal Violet and Methylene Blue of varying degrees of purity have been examined. Large samples of each dye, moreover, which were shown to be of fair purity by analysis, were further purified by successive crystallization from water, alcohol, and water. The spectroscopic behavior of the products thus obtained differed in no material respect from that of the most impure products investigated. SIGNIFICAKCE OF PHENOMENA. In the following discussion reference will be confined primarily to absorption equilibria of the general type exhibited by Crystal Violet and Methylene Blue, in which a transition between definite absorption bands of widely separated location has been clearly established. It will be obvious that 14
THISJOURNAL, 16, 833 (1923).
2-
I
500 520 540 560 WAVE LENGTH
480
580
600
FIQ.IV-RHODAMINE B 1 = 500 parts per million 4 = color base in alcohol 2 = 125 parts per million 5 = color base in benzene 3 = 1 25 Darts Der million
.
.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1924
the specific character of the phenomenon excludes any possible explanation on purely physical grounds. I n this connection it may be noted that the results obtained in general in the present investigation serve to account for certain of the alterations in absorption noted by Kalandek,' and a t the same time to refute the general validity of the hypothesis which he was concerned in establishing. r~ I I I I I I I I 1 1 I I I I
540
560
600 620 WAVE LENGTH
580
640
660
680
FIG.V-METHYLENE BLUE 4 1.25 parts per million
1 = 300 p u t s per million 2 = 100 parts per million 3 26 p u t s per million
-
5 = 125 parts per million (95% alcohol) 6 = dry dye {gelatin)
With t h e consideration to all circumstances it does not appear possible to find an adequate explanation of the phenomenon in question in any other assumption than that of constitutional alteration. Numerous evidences, moreover, have been noted which are indicative of a fundamental connection between the constitution of the dyes examined and their characteristic spectroscopic behavior upon dilution. The decisive influence of constitutional variation a t the amino nitrogen atoms of certain classes of dyes has been particularly evident. Apart from these considerations, it is held as axiomatic by the writer that alteration in absorption necessarily implies constitutional alteration and that the magnitude of the effect under discussion necessitates an assumption of radical molecular rearrangement. In accordance with this view the widely separated absorption bands in question constitute evidence of a radical alteration Tvii hin the dye molecule, involving a rearrangement in the distribution of affinity if not an actual atomic rearrangement. The tautomerism between such bands which has been established in the instances of Crystal Violet, Methylene Blue. and numerous other dyes is accepted as decisive evidence that the dyes in question exist in aqueous solution in a state of tautomerism between two constitutional forms, molecular rearrangement occurring as the concentration of the solution is varied. It appears improbable that variation in concentration should, in itself, constitute an adequate cause of this tautomerism, and it is apparently necessary to consider the possible operation of other factors which are associated with change in concentration. In view of the investigations of Miolati,l5 Hantzsch and Oswald,lG and Pelet-Jolivet and Wild,l7 it may be questioned Ber., 23, 1788 (1890); 28, 1696 (1895). Ibid., 83, 278 (1900). 17 2. Chem. I n d . Kolloide, 3 , 174 (1908).
1)
39
if hydrolytic dissociation plays a role of any general importance in solutions of dyes. It is evident, moreover, that the absorption bands which have been established as characteristic of dilute aqueous solutions do not originate in hydrolytic action, since they are essentially identical with the bands of both concentrated and dilute alcoholic solutions. The evidence excluding electrolytic dissociation appears equally conclusive. The zone of the occurrence of the absorption equilibria a t issue does not coincide with that over which electrolytic dissociation takes place. ElectroIytic dissociation is general with dyes, moreover, in both alcoholic and aqueous solution, whereas the radical modifications in absorption noted are not observed with all dyes and occur, in general, only in aqueous solutions. It does not appear possible to base any plausible hypothesis for the explanation of the observed phenomena upon any assumption of solvation. The possible operation of molecular aggregation, however, may warrant more particular consideration. The hypothesis was advanced by Stenger18 that color and absorption alter with change in size of the physical molecule and that various anomalies in color and absorption may be accounted for on the basis of varying degrees of aggregation of the chemical molecule. , More recently, SheppardO has advanced somewhat similar views correlating absorption and colloidal state. So far as these hypotheses state or imply that change in colloidal state may, in itself, result in the development of new absorption bands or that the development of such bands may be accepted as a criterion of a decided alteration in colloidal aggregation, they are not accepted by the writer. No comprehensive parallel study of the colloidal and spectroscopic characteristics of solutions of dyes has ever been carried out and no thoroughly adequate basis exists for conclusion respecting the effect of change in colloidal state upon absorption. I n the course of the present investigation a welldefined, symmetrical modification in absorptionwas frequently noted with a variety of dyes in passing from dilute alcoholic to dilute aqueous solution. Apart from the minor displacement of the entire band which is normal to the change in solvent, it was observed that the absorption maximum was decidedly depressed and the lower portions of the absorption curve appreciably broadened. The same type of alteration (without displacement) has been observed with a very large number and variety of dyes in passing from dilute to more concentrated aqueous solutions. With increasing concentration in alcoholic solutions, however, this type of modification was not observed or was much less considerable in degree. Solutions of many basic and acid dyes of the triphenylmethane group, which have been made slightly alkaline and in which molecular aggregation may be assumed to have reached extreme limits, apparently afford exaggerated examples of this same effect. Such solutions may show only very faint absorption, although they may appear highly colored when observed in a flask by reflected light. Pending further investigation this type of symmetrical alteration in the absorption band has been accepted by the writer as a criterion of change in molecular aggregation. It may be pointed out that, even if it is assumed that change in colloidal state involves the development of new bands in different spectral locations, this hypothesis will not account for the observed radical modification in absorption under discussion in a satisfactory manner. In view of the progressive character of colloidal phenomena, it would only be logical to assume that a progression in absorption bands would occur. With increasing aggregation, therefore, the original absorption band would be expected to undergo a
18
18
A n n . Physik Chem. (Wiedemann), 33, 577 (1888).
I N D U S T R I A L A N D ENGI NEERING CHEMISTRY
40
Vol. 16, No. 1
however, the suggestion appears warranted that alteration in colloidal state may possibly constitute a factor of influence upon the molecular tautomerism. In a very few instances in the present investigation the symmetrical type of modification of absorption curves without displacement, to which reference has been made, has been observed to accompany dilution. If this phenomenon may be accepted as indicative of solvation, as seems possible, it appears to be necessary to conclude that but little evidence has been obtained of the occurrence of extensive solvation in aqueous solutions of dyes in general.
Apparatus for Providing a Continuous Stream of Hot Distilled Water' By Chester L. Ford STRUCTURAL MATERIAWRESEARCH LABORATORY, CHICAGO, ILL.
WAVE LENGTH FIG. VI-NEW METHYLENE BLUEN 1 1000 parts per million 2 = 40 parts per million 3 1 part per million
-
gradual and progressive displacement and the phenomenon would not assume the character of a transition between two widely separated bands with an entire absence of development of intermediate bands. It is evident, furthermore, that if the absorption bands which are characteristic of concentrated solutions are to be accepted as evidence of decided alterations in colloidal state, the characteristic spectroscopic behavior of the dyes which have been examined should be susceptible of correlation with their colloidal behavior. I n point of fact, no correlation appears possible between the observed phenomena and the accepted colloidal rating of dyes. I n view of these considerations the writer would reject any hypothesis of a fundamental relation between the extreme
WAVE LENGTH FIG.VII-NILE BLUE2 B 1 = 825 parts per million 2 20 parts per million 3 1 part per million
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modifications in absorption observed and colloidal phenomena, even if the opposed hypothesis of an assumption of molecular tautomerism did not appear t o be both necessary and justified. I n further consideration of the evidence which has been accepted as indicative of appreciable alterations in colloidal state with many dyes under the experimental conditions,
T H E R E has been a long-felt want for a steady stream of hot water for washing precipitates without the necessity of blowing into or otherwise stimulating a wash bottle. To meet this need the writer took one of the ordinary variety and modified and added to it as shown in the accompanying illustration. The usual short length of rubber connection a t the nozzle was replaced by a wash h e consisting Disfilled of about 6 feet of gum tubing, a Wafer pinch clamp, and a rounded nozzle. To provide a reserve supply of water, an ordinary acid bottIe, B, is inverted over the flask and connected to it by the tube C , which extends from the bottom of B to about halfway to the bottom of the boiling flask A . To fill the apparatus, the tube D, which serves as a steam-escape vent when the water is boiling, is connected to the distilled water supply line G. If distilled water is supplied under sufficient pressure, opening clamp E allows the system to fill to a little below the level of the air tube F. If there is not sufficient pressure, suction is applied below E. The tube F reaches to the upper end of the bottle, but the water level is brought only to within an inch of this point. After filling, clamp E is closed, so that the water will FIG. 1 flow into flask A only as the water level falls below the level of connecting tube C. The various units were all attached to a 0.5-inch steel rod, 40 inches long, mounted on a shelf 16 inches above the top of the table. This has been found to give sufficient pressure for all ordinary washing. By regulating the amount of heat applied, it is possible to keep the water in the flask at, or close to, the boiling point, even when a considerable stream of water is being drawn off. One of the outfits now in use in this laboratory gives very satisfactory results with two wash lines instead of one. After the rubber once becomes heated there is very little loss of heat and the wash water delivered from the nozzle is close to the boiling point. 1
Received November 26, 1923.
