A LECTURE EXPERIMENT
on DYEING'
GRAHAM COOK Albright College, Reading, Pennsylvania
M
ANY introductory courses in chemistry, particularly those designated as "general" chemistry courses, include a certain amount of organic chemistry, the admitted objective being to give to the student some appreciation of the field of organic chemistry and of some organic industrial processes. This material usually includes some of the simple fundamentals of the chemistry of dyeing, and also studies of some of the more common natural and synthetic fibers. We have used with much success a lecture demonstration which in one experiment illustrates some of these fundamentals of dyeing, as well as the difference in the chemical nature of diierent fibers. It is a demonstration which never fails to stimulate and arouse the interest of the student. The procedure used, known as cross-dyeing, is a common one in the textileindustry. I t has also been used successfully as a demonstration elsewhere, notably by the traveling chemical "show" of the Museum of the Franklin Institute of Philadelphia. It seems wise to suggest to teachers of chemistry generally the use of such a demonstration and to make easily available the necessary directions and precautions. In this experiment three kinds of fabric (usually sewed together) are put into a dye bath, dyed for a short while, and then taken out of the bath red, white, and blue. Various other col6r combinations are possible, but this seems to be the mo& popular one. No complicated apparatus is required, the materials are easily available, and the time needed is well within usual lecture period requirements. After the water is hot, the procedure takes less than five minutes. This amount of time will produce shades which are deep enough if the fabrics are displayed wet. All of the materials may be secured locally except the dyes; two specific sources of these that we have found satisfactory are suggested below. For the fabrics we use a pure dye crepe silk, a viscose rayon crepe, and a cellulose acetate taffeta, purchased in a local department store. If not available locally, they can be purchased through one of the larger mail order houses. Sometimes acetate rayon sold as such is a mixture of acetate and viscose rayon; the heavy m e t a s are usually pure acetate fiber. In any event
-
1 Presented before the Division of Chemical Education at the ninety-sewnth meeting of the A. C. S., Baltimore. Maryland. April 6. 1939. The procedure described in this paper was demonstrated before the Division.
it is wise to test the fabrics beforehand. The pieces demonstrated are about ten inches square, with the acetate sewed between the rayon and the silk. In our procedure, we use a rayon, or direct cotton blue for the rayon, a silk scarlet dye for the silk, and leave the acetate undyed. For the rayon we use Diamine Sky Blue FF (Colour Index No. 518)=,and for the silk, a special dye, Silk Scarlet 3B. This latter dye is manufactured only by the Althouse Chemical Company of Reading, Pennsylvania. Both dyes may be purchased directly from them. We have found these two dyes to be the most satisfactory, and to be the most nearly "fool-proof." With an alkaline bath, and sodium sulfate as the salting out agent, neither of these dyes will stain the cellulose acetate fibers at all. They come out perfectly white. I t is necessary to use soap or some other surface active agent. This not only hastens the dyeing process, but also helps to remove a certain amount of the finishing materials that may be found on the fabrics as purchased. Some of the, newer surface active agents on the mafket give excellent results. We have used the commercial product "Dreft" with much success. Ordinary soap powders, such as "Rinso," "Chipso," and so forth, work very well. It is also possible to get fairly good results by simply using sodium carbonate to make the bath alkaline. Where extreme hardness of the water is experienced, it is wise to use distilled water. The specific directions for a typical experiment, using the Althouse dyes, are given here. In all cases percentages given always mean percentage by weight of the materials dyed. I t is-therefore uecessary to weigh the fabrics beforehand. Two per cent. Diamine Sky Blue FF Two per cent. Althouse Silk Scarlet 3B Five per cent. soap flakes Fifteen per cent. sodium sulfate, anhydrous 20:l bath ratio We use pieces of fabric about ten inches square. In one case this amount of rayon weighed six grams, cellulose acetate six grams, and silk five grams. For these quantities the volume of the dye bath is 340-350 ml. The water is brought to a temperature of 85' C. and 0.12 g. of Diamine Sky Blue FF, 0.10 g. of Silk ' R o w ~ .Editor, "Colour index," The Society of Dyers and Colonrists. Bradford, Yorkshire, England, 1924.
330
Scarlet 3B, and 0.85 g. soap flakes added and completely goods continually dwing the dyeing operation. If a dissolved. The fabrics are then introduced and wn- temperature of 85' C. is exceeded, the cellulose acetate stantly agitated. Next, 2.5 g. of anhydrous sodium fabric might be damaged, with resulting loss of luster. sulfate are added, either in the solid form or in con- I t is easier to make up solutions of the dyes beforehand, centrated solution. The dyes go on to the fibers very and measure the quantities volumetrically. In the quickly d t e r this; as soon as the shades become deep demonstration performed before the Division of Chemienough, the fabrics are taken from,the bath, rinsed cal Education at Baltimore, the quantities of all materials were simply estimated and added in the solid form. quickly once or twice, and then displayed. We have also used successfully two dyes furnished This can be done with a little experience. Other variations of the experiment are possible. by the du Pont Company. The dyes they suggest are just the reverse of those named above, a blue dye for the In one case we made a very close approximation of the silk, "Pontacyl" Brilliant Blue 6B, and a red dye for United States flag. This was made by sewing together the rayon, "Pontamine" Fast Scarlet 4BA, Colour a field of rayon, and alternate stripsof silk and cellulose Index No. 326. They may be secured from the E. I. acetate. We also point out in the demonstration that du Pont de Nemours Company, Wilmington, Dela- these dyes may be used as a test for the various kinds of fibers. This can be most strikingly shown with ware. The quantities necessary are as follows. fabrics made of two or more kinds of fibers. Other fibers may he dyed: cotton and rayon will dye the same, One per cent. soap flakes One per cent. soda ash and silk and wool the same. The experiment not only Three per cent. "Pontamine" Fast Scarlet 4BA demonstrates the specific affinity of the dyestuffs for the different fiben, but it also shows the "salting out" Two per cent. "Pontacyl" Brilliant Blue 6B Twenty per cent. sodium chloride effect. Other variations of the experiment will suggest themselves. 40:l bath ratio We have also adapted the experiment for the use of The procedure is the same as with the other dyes; it students in the laboratory. We issue two-inch squares is necessary here to keep pretty close to these percent- of the three k i d s of material, and make up stock ages of materials to get good results, particularly for solutions of the dyes, soap, and salt. A slightly higher the soap and soda ash. bath ratio, 40:1, is used. The students weigh the The experiment as described is almost "failur& cloth and calculate the necessary amounts of materials proof." The percentages given, particularly for the to use. The time of dyeing is increased to give deeper dyes suggested, may be varied considerably. If neces- shades, as the students dry the samples and keep them. sary, extra dyestuff, or salt, may be added during the With small pieces of cloth, the expenditure for large course of the demonstration, if the quantities first used classes is not pm,hibitive. T h e amount of dyestuff do not produce satisfactory shades. In fact the quanti- needed is not large, and the dyes suggested are not exties of materials suggested are more than needed for pensive when bought in one pound lots. In closing, I should like to acknowledge the valuable satisfactory dyeing, hut it is often necessary in lecture demonstration to use a more or less "sloppimetric" assistance given by Mr. Harold C. Gift, of the Althouse method in order to get the essential speed. There are Chemical Company, and Mr. A. G. Bruinier, Jr., of the several precautions necessary to get even dyeing, the E. I. du Pont de Nemours and Compatly, who assisted most important of which is to agitate orff"work" the materially in the development of this experiment.
-
