RHYTHMIC ET’APORATIOS RIXGS O F ORBNGE I1
AND FAST RED B BY EARL
c. H.
DAVIES, KEXNETH TAYLOR, AND E.
w. RIBLETT*
Introduction The first study of the peculiar structures obtained when two dissolved substances are allowed to react slowly to form a precipitate was made by Rungel in 1865, when he was attempting to add stiffness or rigidity to blotting papers. He conceived the idea of forming precipitates between the fibres of the paper by first saturating the paper with some soluble compound that would later be precipitated by the diffusion of a second soluble compound into the paper. I n the course of his investigations he noticed peculiarities in the form and shape of the precipitates, which peculiarities he found t o be a function of the rates of diffusion. Ord,* in 1869, accidentally obtained other growth forms when he allowed ammonium oxalate to diffuse into isinglass which was slightly impregnated with calcium chloride. The insoluble calcium oxalate was obtained in some very fantastic forms, quite different from those obtained when the two reacting salts were mixed in solution. While experimenting with diffusion phenomena, Lupton3 noticed that in certain cases layers or rings were produced. However, he merely mentioned their occasional occurrence and did not attempt to investigate them. It remained for Liesegangl in 1896, to report his exhaustive investigations of ring formation in gels. He is the first author to give exact data upon these ring structures, and is among the first to point out t’heir significance in explanation of geological diffusion phenomena. His first preparations were made by placing a drop of silver nitrate solution upon a glass plate that had been coated with gelat,in impregnated with potassium bichromate. This gave a series of concentric rings consisting of insoluble silver chromate, the rings being spaced a t wider intervals apart in proportion as the distance from the center increased. I n 1914, E. Kiisters reported and described the rhythmic crystallizations obtained when trisodium orthophosphate, cupric sulfate, ferrous sulfate, potassium ferrocyanide, and ammonium sulfate separated from gelatin solutions on drying at ordinary temperatures. This is thought to be the * Presented a t the Colloid Division of the .Imerican Chemical Society a t Minneapolis September 1929. Runge: “Der Bildungtrieb der Stoffe” (1865). Ord: “The Influence of Colloids on Crystal Formation” (1879). Lupton: Kature, 47, 13 (1892). Liesegang: “Phot. Archiv,” 1896, 321. 5 E. Kiister: Kolloid-Z., 14, 307 (1914).
RHYTHMIC EVAPORATION RINGS
8 43
earliest reference in the literature to rhythmic bands by evaporation. A year later, A. v. Fischer' obtained rhythmic agate-like structures by solidifying very thin layers of molten sulfur. I n 1922,E. C. H. Davies2 reported rhythmic bands of dyes upon filter paper, cotton cloth, and unglazed porcelain when dilute solutions of dyes were allowed t o evaporate at constant temperature. Hans Kagi,3 in 1923, found that methyl a-benzoacetoacetate was an excellent example of substances which show rhythmic crystallization. The crystallization occurred a t the rate of about one centimeter per minute and could be followed in detail under the microscope. The rings varied in width from a fraction of a millimeter to five millimeters, depending upon the amount of solvent remaining with the crystals, the amount of ester per unit of surface, and the rate of evaporation. He also noted that only freshly prepared solutions of the racemic ester in benzene gave satisfactory crystallization forms. Garner and Randall4reported that, when in the form of thin films, myristic, lauric, undecoic, and decoic. acids crystallized in a rhythmic manner, due t o the formation of a solid skin which wrinkled, giving a waved surface. They ascribed the formation of the solid skin to differences between the temperatures of solidifications of the material on the liquid-air and liquid-glass surfaces. They attempted to prove orientation by showing whether the rhythmic crystals were isomerides of the natural form. Cooling curves for this purpose gave two enantiotropic modifications. I n a later article, Davies5 reported formation of evaporation rings by allowing a suitable dye solution to evaporate from a watch glass. He studied some 40 dyes and about' I j other colloidal solutions, but purposely did not give any quantitative data. Over IOO solutions have been tried in this laboratory. The object of the present study was to ascertain some of the quantitative relationships between the number of evaporation rings and the conditions affecting the surface of the lens, the concentration of solution, the curvature of the container, temperature of evaporation, and surface tension. This investigation comprises more than IOO,OOO ring counts. Preparation of Materials The water was prepared by partial condensation from a Barnstead still, the rate of condensation being such that the collected portion of water was hot. Comparison was made of the use of t,his water wit,h that of the same water after boiling to two-thirds of the original volume; with that of ordinary distilled water; and with tap water. It was found that the hot mater obtained from partial condensation from the Barnstead still contained nothing which influenced the number of evaporation rings, and its use was adopted for all subsequent experiments. Frequent tests on the pH of this water gave 6.9-7.0. Fischer: Kolloid-Z., 16, 19(1915). Davies: J. Am. Chem. Soc., 44,z j o j (1922). Kagi: Helv. Chim. Act., 6,264; Kolloid-Z., 33, 284 (1923). ' Garner and Randall: J. Chem. Soc., 125, 369 (1924). Davies: Proc. W. Va. h a d . Science, (,1928). ?
844
EARL C. H . DAVIES, KENNETH TAYLOR, AND E . W. RIBLETT
Orange 11 was made partly in this laboratory and partly in the Eastman Kodak Research Laboratories. That part which was prepared in this laboratory was by the following scheme:
OH
1 2 Orange I1 The sulfanilic acid was dissolved in water by careful addition of caustic soda solution. Ice was added until the temperature was about 5°C. The required amount of hydrochloric acid was poured in and a solution of sodium nitrite added slowly. Tests were made from time to time with starch iodide paper, a slightly blue color indicating that enough sodium nitrite had been added. The @-naphthol was dissolved in sodium hydroxide solution and the solution cooled to about I j O C . The diazo solution was added slowly with stirring. This was stirred for an hour longer; salt added; and the dye filtered and dried. It was recrystallized three times. To check the purity of the Orange 11,a quantity of the purest dye obtainable was secured from Eastman Kodak Research Laboratories. Some of the latter dye was recrystallized, and the product gave results similar to those from the dye made in this laboratory. Fast Red B was made in this laboratory, according to the following scheme:
OH SO,Na
SOsNa Fast Red B
845
RHYTHMIC EVAPORATIOK RIXGS
The a-naphthylamine was dissolved in hot water containing a small amount of hydrochloric acid and the solution cooled to o°C. The sodium nitrite dissolved in a small amount of water was poured in rather quickly. This diazo solution was then added slowly to the solution of the sodium salt of a-naphthol-3:6 disulphonic acid (R-salt). The latter solution was prepared by dissolving the calculated amount of R-salt in a large amount of water containing a few grams of sodium hydroxide, The mixture was well stirred during the additio6, and for one hour afterward. The solution was heated to 8 0 O C . and a small amount of sodium chloride added to precipitate the dye, which was then filtered off. The dye was redissolved, twice recrystallized, the resultant product dissolved, and the most soluble and least soluble portions rejected. The part retained formed a gel which easily gave up its water, leaving a very fine, brown powder. n-Butyric acid was Eastman Kodak Company's best grade (#io). It was further purified by distilling through a Glinsky tube, the first and last fifths being discarded. The middle portion was redistilled and the first and last fifths again discarded. The portion used boiled a t 161.5-163OC. under 730 mm. pressure TABLEI Radius of Curvature in Millimeters ft-inch glsws I I1 I2
I4 16
17 I8 I9 24 26 It
16t I7t I9t
Spherometer No. I 1 = 4 o . w mm.
It
6t 7t
P=
2
Average
93.24 93.48 93.36 93.45 93.33 93.48 93.24 93.20 93.33 93.55 93.20 93.03 92 ' 58 92.80
91.67 91 .99 92.16 92.24 92.36 92.38 92.08 92 92.34 91.61 91.27 90.97 90.99 90.91
92.45 92.74 92.76 92 . 8 5 92 . 8 5 92.93 92.66 92.63 92 .83 92.58 92.23 92 .oo 91.78 91.85
156.13 155.68 755.77 155.77 163.34 160.54 162.22
150.59 150.64 150.47 '50.53 156.57 155.99 156.25
153.13 153.16 153. I 2 153.15 159.95 158.26 159.23
5-inch glasses 6 7 39 63
S herometer No. 48.12 mm.
846
EARL C . H. DAVIES, KENSETH TAYLOR, AND E. W. RIBLETT
Abiettc acid was Eastman Kodak Company’s best grade (81356) and was used without further purification. Ethyl ether used for dissolving the abietic acid was C.S.P. obtained from the Will Corporation. Part of this was redistilled but gave the same results as the original. Watch glasses. Out of over 1,000watch glasses examined for curvature, 300 of apparently uniform curvature were tested with spherometecs. Results in Table I for the 2 1 best watch glasses show that even after this amount of work, although uniform among themselves, they were not spherically curved. That is the watch glasses were flatter near the center. These radii were calculated by substitution in the formula: l2 r = h-+-2
6h
where r is the radius of curvature in millimeters, h is the spherometer reading in millimeters, and 1 is the distance between the tripod points of spherometer. Optical lewes, about 4. j cm. in diameter, were obtained from Bausch and Lomb Optical Go. They were highly polished and ground to uniform curvature. These lenses were of eleven curvatures, the radius of curvature ranging from 24.99 mm. to 115.48 mm. There were three duplicate lenses of each curvature. The curvature was measured with a tripod spherometer, the results of which are shown in Table I1
TABLE I1 Radius of Curvature in Millimeters Lens number
Radius of curvature
A B TA
115.48 81.42
70.16 59.48
C TB D
j0.16
44.27 40,87
TC E TD F TE
35.35
30.75 27.59 24.99
Experimental General Procedure.-All lenses, pipettes, and containers, were immersed in fresh cold cleaning mixture for a t least twelve hours or in hot cleaning mixture for at least three hours. They were then thoroughly rinsed with the special distilled water, and dried in the electric oven a t 5 0 T . The lenses were not touched with the fingers.
RHTTHMIC EVAPORATIOS R I S G S
847
Calibrated pipettes were used in adding the dye solution to the lenses and evaporation was carried out in a Freas electric oven a t constant temperature. LOWForce of Adhesion of Orange I I and Glass.-On clean lenses the number of evaporation rings of Orange I1 were sensitive to slight differences in washing and drying, due to the small force of adhesion between the solid Orange I1 and the surface of the lenses. This irregularity was clearly shown in a series of preliminary experiments with Orange 11. These experiments comprised over 5,000 ring counts on 16j lenses and watch glasses. For the sake of brevity, tables are omitted but the conclusions are as follows. I. The number of evaporation rings increased Prith concentration. This is contrary t o all results which have been obtained with evaporation rings which adhere well to the surface of the evaporating dish. 2. Orange I1 solutions gave more rings on flatter than on steeper dishes. This is also contrary to all results obtained with evaporation rings which adhere well to the lens. KO rings mere obtained with solutions of Orange I1 when special care was taken to clean the lenses. 3. The force of adhesion between solid Orange I1 and glass is so slight that a foundation film is essential for a quantitative study of evaporation rings. The Foundatton Fzlni.-JThereas solutions of Fast Red B of every degree of purity gave evaporation rings on all surfaces tried, solutions of Orange I1 gave good rhythmic evaporation rings only under certain definite conditions. For example, when the special optical lenses were carefully cleaned, Orange I1 gave but one band near the center of the lens. On the other hand, where the lens was carelessly cleaned or rubbed with the hand it gave very good rings. The difference between the formation of no rings with the pure Orange I1 on clean lenses and the formation of rhythmic evaporation rings in the presence of impurities might be due to one or more of three factors: I . The condition of the surface of the lens itself; 2 . The presence of a foreign substance in the solution; 3. The presence of a surface film on the dye solution. Each of these was studied. Adsorbed Gas.-Since the gas would be air in the ordinary experiments, and since the amount adsorbed would be greatest when the lens was driest, a comparison was made between the number of evaporation rings produced on duplicate lenses, on one set of which the dye solution was added immediately after washing, whereas the other two sets of lenses were kept over phosphorus pentoxide a t 5o°C. for as much as two days. This extra drying had no effect on the number of evaporation rings. A film of adsorbed air on the glasses is not responsible for rhythmic evaporation rings of Orange 11. Adsorbed Lzpuids.-The impurity responsible for the rhythmic evaporation rings of Orange I1 on carelessly cleaned lenses might be a liquid which assisted in sticking the evaporation rings on the glass surface. This liquid could come either from vapors or direct addition, as when the lens is rubbed by the hand, which leaves a thin oily film on the glass. Liquids studied were:
848
EARL C . H. DAVIES, KENNETH TAYLOR, A S D E. W. RIBLETT
water, methyl, ethyl, n-propyl, n-amyl, and n-octyl alcohols, geraniol, carvacrol, n-butyric acid, n-caproic acid, and stearic acid. I n order to allow the vapors of water and alcohols to condense upon the lenses, 0.1 gram of each liquid was put in an open weighing bottle and enclosed, together with the lenses, in a 2 5 0 cc. beaker, and allowed to heat for at least one hour at jo°C. A duplicate set was allowed to heat in a similar way at 15g'C. A measured volume of 0.1% Orange I1 was added to each lens and allowed to evaporate a t 5o°C. I n case of the acids, the exposure of lenses to the vapors was for more than I j hours a t jo°C. Results showed that rhythmic evaporation rings of Orange I1 were probably not due to vapors adsorbed from the air. Adsorbed Solids.-The impurity responsible for the rhythmic evaporation rings of Orange I1 on carelessly cleaned lenses might be a solid which assisted in sticking the evaporation rings on the glass surface. Since camphor sublimes a t temperatures of 50' and I jo°C. lenses exposed to these vapors should, when cooled t o ordinary temperatures, be coated with a thin film of solid camphor, but this did not result in formation of rhythmic evaporation rings of Orange 11. Clean dry lenses, covered and uncovered, were exposed to laboratory air for about eighteen hours, and although the deposition of solid dust on the uncovered lenses did not materially influence the formation of evaporation rings on these same lenses, it was thought probable that a closely adhering solid film might affect the number of these rings. Rosin consists of about 9470 abietic acid (CI(IHZBOP), whose physical characteristics, including its insolubility in water, are such that it seemed probable that a thin film of abietic acid on the surface of the lenses might assist in causing evaporation rings of Orange I1 to adhere to the lenses. The clean dry lenses were dipped into a 0 . 1 0 4 7 ~solution of abietic acid in ethyl ether, the excess being allowed to drain off while keeping the lenses nearly vertical just above the surface of the solution. The transparent film of abietic acid in contact with the Orange I1 was found to weigh about 0.0001 gram. Electrical Condition of the Surface of Lens.-Cataphoresis experiments show that in a solution of Orange I1 the particles of dye are negatively charged. It is conceivable that the surface of the lens might be charged with negative electricity, resulting from friction or from adsorbed substances, and that this negative charge would operate against the adhesion of negatively charged particles of Orange I1 on the surface of the lenses. Water on glass gives a negative charge to the glass. When dry glass is rubbed with silk the surface of the glass becomes positive. This would remove the negative charge from the glass and the formation of rings might be facilitated providing the glass retained its positive charge after the dye solution had been added. Experiments were carried out in which dry lenses were rubbed with clean silk. Good rhythmic evaporation rings of Orange I1 were then produced. Somewhat similar results were obtained when dry lenses were rubbed with
849
RHYTHMIC EVAPORATION RINGS
the fingers, absorbent paper, absorbent cotton, and glass wool. Experiments with lenses of assorted curvatures showed the following increase in number of rings of Orange I1 resulting from about one minute of vigorous rubbing; fingers 13; silk 11; cotton, 7 ; absorbent paper 7 ; glass wool 6. I n order to determine if the abrasion of the surface caused the evaporation rings to form, the lenses were cleaned in the usual manner and Orange I1 solution again evaporated from them. No rings were obtained. Effect of Concentration on the Number of Rings.-In all experiments for which tables on evaporation rings are given, only the Bausch and Lomb optical lenses were used. For Orange I1 they were coated with the thin transparent film of solid abietic acid. Averages in Table TI1 and Fig. I show that the number of evaporation rings of Orange I1 and Fast Red B are fewer for concentsratedthan for dilute solutions.
TABLE I11 Concentration Effects Radius of Curvature
70.16 50.16 40.98 30.75 24.99
Average Radius of Curvature
S u m b e r of rings from Orange I1 ( 3 . 1 2 5 c c . a t 50°C.)
16.06
10,s
31.49 41.83 44.50
18.24 20.53 21.38
45.41 31.36
23'19 19.88
11.6 11.8 11.7 14.0 11.9
5.0070
1.00%
0.50%
o o
o
5.16 6.50 7.00 8.17
11.5
9.83
o
9 9
7.32
0
7.5 9.j 10.0
11
Sumber or rings from Fast Red B (2.246 cc. a t 50°C.) 0.05% 0.10% 0.2070 0.30% 0.50% 0.75%
0 . 0 0 0 5 ~ c0.005%
59.48
45
41.27
47 49 66 47
Average
0.25%
26. j 8
115.48 81.42
35.35 27.59
0.10%
0.01%
33
35
23
41
40 j4
27
19 23
29
24
j7
28
21
61
32
70
53
12
12
7
~j
IO
~j
11
26
17 18 17 19
34
27
18
29
2 1
I;
14
11
~j
11
15 14
IO
II
0
o
1.005
7 8 8 8 8
4 6 6
8 8
5
5 5 j
There are no rings for a saturated solution, the number increasing with dilution, first slowly and then more rapidly. With solutions of Orange I1 more dilute than O . O I ~ & the rings were blurred, while with Fast Red B evaporation rings were distinct, but discontinuous, even a t a dilution of 0 . 0 0 0 j ~ ~The . number of evaporation rings of Orange I1 and Fast Red €3 varies inversely with the concentration of the solution. Effect of Curvature on the Xumber of Rings:-Table I V summarizes the results of about 70,000 ring counts.
EARL C. H. DAVIES, KEXNETH TAYLOR, AND E . W RIBLETT
850
Column I gives the radius of curvature. The steepest lens had a radius of curvature of 25 mm. while the flattest had a radius of curvature of I I 5.5 mm. Column z contains the average number of rings obtained for all concentrations of the pure dyes. I n column 3 are averages for 0.1% dye solution a t different Fast Red B containing temperatures. Column 4 gives averages for 0.17~ varying amounts of n-butyric acid. The last column in Table IV gives the mean of all these averages for all concentrations, all temperatures, and in the presence of n-butyric acid.
0.1
0.2
0.3 0 ~ 4 0.5 0.6 0.7 0.8 PER CENT COIYCENTRAT/ON OF DYE
0.9
FIG.I Variation in number of rings with concentration
TABLE IT' Curvature Effects Radius of curvature
Concentration series 5 0 T .
Temperature series
Butyric acid series j0"C.
Grand average
Orange I1 (3.12j cc.) .16 50.16 40.87 30.75 24.99 jo
11.9; 14.06
17.34 18.51 19.61
14.24
16.54 18.76 19.j1
16.41 18.52 I9,3i 20.43
20.22
21.25
Fast Red B (2.246 cc) 115.48 81.42 59.48
20
I9
30
22
44.27
24 28 28
35.35 27.59
30 35
22
35 37 41
2?.
42
26
43
23
1.0
RHYTHMIC EVAPORATIOE RIKGS
85 1
These "grand averages" are plotted in Fig. z which also contains curves for 0.1% dyes a t 5o°C. These curves show that the number of evaporation rings increases as the lenses become more highly curved. All these curves seem t o be straight lines. Some preliminary study has been made of curvatures greater and less than those shown in Fig, 2. Microscope cover-glasses at different angles were put in open weighing bottles containing dye solution. Evaporation was carried out a t 5oOC. With both Orange I1 and Fast Red B evaporation rings were obtained on the vertical wall and on the upper surfaces of the slanting side of the glass slides. That this limiting angle for rings is less than that of a
I'
FIQ.2
plane perpendicular to the surface of the dye solution is shown by the fact that rings of Fast Red B were formed on the inside walls of a small Erlenmeyer flask. A highly interesting experiment was carried out as follows. .4 3-inch watch glass with a hole in the center was put, convex side up, inside a crystallizing dish of very nearly the same diameter. A 0.1% solution of Orange I1 was poured into the dish until the watch glass was just covered. Evaporation at 5 0 T . left good rhythmic rings on the upper surface but none on the under surface, where the angle of contact was sharp. Gravity would also help t o pull the dye away from the under surface. E$& of Temperature.--Using optical lenses coated with a film of abietic acid, 0.17' Orange I1 solution was evaporated at each of three different temperatures-32, jo, and 85OC. From the average shown in Table T it I S seen that the number of evaporation rings of Orange I1 increases with temperature. I t is possible that a t least a part of this large increase in number of rings with temperature may have been due to the action of heat on the film of Fast Red B at the same temperatures there was a abietic acid. With 0.17~ slight decrease in the number of evaporation rings for the higher temperatures.
EARL C. H DAVIES, KENNETH TAYLOP, AXD E. W. RIBLETT
TABLE V Temperature Effects Radius of curvature
70.16 50,16 40.87 30.75 24.99 Average 115.48 81.42 59.48 44.27 35.35 27 4 9 Average
Number of rings 32°C. 12.33
14.44 14.91 15.36
50°C.
Orange I1 ( 3 . 1 2 5 cc.) 16.06 18.24 20.53
85°C. 21.22
23.61 23.69 24.91 25.56
20
21.38 I9 19.88 Fast Red B (2.246cc.) I9
24
23
20
24 23
24 24
20
17
.oo
14.81
23
'
23 .So
I8 21
25
26
23
27
27
24
24
24
21
E$ect of Surface Tenston.-In attempting to explain evaporation rings, one of the first things thought of is what relationship there might be between ring formation and surface tension. Surface tension changes will result from either temperature change, or the addition of almost any impurity to the dye solution. The quantitative relationship between surface tension and the temperature of evaporation of Fast Red B has not yet been worked out, but it has already been shown that the number of rings decreases with a rise in temperature. n-Butyric acid lowers the surface tension of Fast Red B from 72.39 dynes for pure 0.15;solution to 58.67 dynes for 0.1% dye solution containing I % butyric acid. The corresponding numbers of evaporation rings are 24 for the pure dye and 83 for the solution containing butyric acid. That this increase in the number of evaporation rings, produced in the presence of n-butyric acid, is not entirely dependent upon surface tension seems apparent from the fact that similar experiments with 0.1% Fast Red B containing the same normalities of hydrochloric acid instead of butyric acid gave decreases in the number of evaporation rings (from 2 I for pure dye to 16 for 0.c57N HCl and 1 2 for the o.085N HCl), although the HCl was found to lower the surface tension of the dye solution. Furthermore, the surface Orange I1 is lowered by n-butyric acid while the number of tension of 0.17~ evaporation rings is nearly the same as for pure Orange 11. The behavior of n-butyric acid in 0.1% Fast Red B is interesting in that increasing concentrations of n-butyric acid caused rapid change in the number of evaporation rings. From 0.02% to 0.67~the increase is slow and linear. Above 0.67~the increase in the number of rings is very much greater. Thus ~ acid the number of lings inbetween 0.0273 butyric acid and 0 . 6 7 butyric creases from 26 to 2 9 ; further change in concentration from 0.6% to 1'7, butyric acid increases the number of rings from 29 to 83.
853
RHYTHNIC EVAPORATION RIKGS
TABLEVI Effect of Butyric Acid on Per cent butyric acid
o
Fast Red B
0.1%
0.65 0.75
0.30
0.50
27
25
20
19
15
o
0
2
8
15
25
83
27
28
34
40
83
0.5' 0.5 0.6 0.7 0.8 0.7 PER CENT h-BUTYRfC ACID FIG.3 Variation in number of rings from 0.1% Fast Red B with Concentration of n-butyric acid at 50" C
1.0
Number of wide rings
21
Number of fine rings
0
Total number of rings
21
0.02
25
0
25
0.10
2 j
1.00
I
10.
./". OJ
0.2
0.3
-0-8-
-0-
Average total number of rings Average number of very fine rings Average number of large rings
Beginning a t a concentration of O.I
