December, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
least a not inconsiderable penetrative power. Though not very strongly bactericidal, they are, even in weak solutions, highly bacteriostatic, and their study has brought out the importance in therapeutics of this somewhat new conception of bacteriostasis (a direct development of the gentian violet studies) which appears to be leading us away somewhat from the Ehrlich conception of the necessity of a sterilisans mngna. The dyes are less toxic for many animal cells than they are for bacteria; they appear to be pretty well tolerated even by the blood stream. Conclusion In stating these qualities of the aniline dyes I have answered the questions put at the beginning of this paper as t o the relation of the dyes to the ideal antiseptic and have indicated the probable course of future development in
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this field. It seems hardly likely that this development will occur without considerable modification in the underlying conceptions of chemotherapy. Reference has already been made to the significance of the idea of bacteriostasis for the theory of a skrilisans magna. Much skepticism has arisen also as to the existence of chemoceptors, and the allied hypothetical machinery of affinities. Even the idea that the effective contact between chemical substance and microorganism takes place in the blood stream is now open to considerable doubt. But however these conceptions of Ehrlich are modified, or even if they are ultimately abandoned, they have represented one of the greatest advances in the history of medicine. They provided a new starting point. From this starting point investigation of the aniline dyes has proceeded a considerable distance. It promises to go much further in the near future.
The Work of the Bureau of Standards on Dyes' By Wm. D. Appel BURSAKIO F S T A N D A R D S , WASHINGTON, D.
HE work of the Bureau of Standards on dyes is an outgrowth of the work of the Colorimetry Section of the bureau on the standardization of colors by spectrophotometric methods. The color of a dye in solution or upon fabric can be fundamentally specified only by the spectral transmissive or reflective properties, respectively, measurements which this section is undoubtedly better qualified to make than any other laboratory in the country. The bureau first worked in cooperation with the Bureau of Chemistry, represented by W. E. Mathewson, on spectrophotometric data for seven permitted food dyes in the visible, ultra-violet, and infra-red.L* The need for a dye chemist st the Bureau of Standards who should be responsible for the chemical end of the work was evident and a dye laboratory was established in the Chemistry Division in February, 1922. Mathewson was placed in charge of this laboratory but resigned after a few months. The writer has carried on the work since September, 1922, with the help, during part .of the time, of Wallace R. Brode and I. M. Welch.
T
Spectrophotometric Work
It is natural that the application of spectrophotometry t o dye problems has been one of the principd interests of the laboratory. Although in the past an enormous amount sf work has been done on the relation between the spectral absorption and the chemical constitution of dyes, the greater part of it has been qualitative. Spectrophotometric measurements are quantitative, independent of the observer or instrument, and are a direct measure of the most important property of a dye, its color. Carried into the ultra-violet they are significantly related to the constitution of the dye. Such measurements for a dye of known constitution, in a number of solvents, are a permanent and unique record of that dye. In connection with other tests they are the best means for the identification and quantitative evaluation of dyes. All of the precise spectrophotometric work has been done with the instruments of the Colorimetry Section either by the staff of that section or with its cooperation. In addition to the measurements of the seven permitted food dyes, 1 Published by permission of the Director of the National Bureau of Standards, U. S. Department of Commerce. Numbers in t e x t refer to bibliography at end of paper.
*
e.
samples of known purity of ten important textile dyeslo have been measured throughout the visible and in the ultra-violet and infra-red, and some fifty other textile dyes have been measured in the visible. This work is going slowly because of the limited personnel, but will eventually result in a compre hensive atlas of standard absorption curves. A quantitative study of the effect of substituent groups on the absorption of simple azo dyes has been undertaken in this laboratory by Brode. He has already reported on the mother substance, azobenzene,' on benzeneazopheno1,S and on the effect of the methyl group in mono- and dimethyl derivatives of benzeneazophenol.ll Measurable differences in absorption which can be associated with the position of the methyl group have been observed. This work is being extended to the chloro, bromo, nitro, amino, carboxy, and sulfonic acid derivatives. Preliminary work in which the effect of some thirty solvents on the absorption of benzeneazophenol was studiedb gave the important observation that the presence of even less than 1per cent of alcohol in benzene or in carbon tetrachloride used as a solvent for the dye leads to the characteristic absorption of the dye dissolved in alcohol alone. Organic solvents of the usual C. P. grade frequently contain small amounts of other solvents which may influence the absorption of a dye dissolved in them. This must be borne in mind if these solvents are to be used in making spectrophotometric measurements on dyes. Evaluation of Dyes
A more immediately practical application of spectrophotometry has been a study of its use in the evaluation of commercial dye^.^#^ Like the well-known titanous chloride titration, with which it has been compared, this method is convenient, rapid, and precise. Unfortunately, neither of the two methods can be relied upon to give the same result as the practical dyeing test on dyes of commercial quality, though they usually do give a good indication of what may be expected in that test. It is probable that where the two methods agree the same result will be obtained by the dyeing test.6 Unlike the titration method, the spectrophotometric method gives some indication of the quality of the dye. It may be used to advantage in conjunction with the dyeing test in the identification and evaluation of the subsidiary
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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coloring matters present in commercial dyes.* It is especially useful for relatively pure dyes, very small samples, and dye mixtures. Since the dyeing method of test is standard for practical purposes, it has received attention. A method has been developed in which flock-that is, finely chopped fiberis substituted for the skein or piece of cloth ordinarily used, and is dyed in a closed bath with mechanical agitation and controlled temperature. This method permits a long series of strictly quantitative and comparable dyeings to be made. It is quicker than the ordinary methods2 Standard Fastness Tests
There is a very obvious need for standard methods for testing the fastness of dyed materials. All the way from the research chemist working on new dyes to the ultimate user of dyed fabrics, fastness is a most important consideration. Hundreds of fastness tests are made daily in the laboratories of dye manufacturers, textile dyers, and distributing branches of the industry; yet, because of the diversity in methods and nomenclature it is difficult, if not quite impossible, to correlate the results obtained and to express or record them in any very satisfactory form. Work on methods for testing fastness to light and fastness to washing has been in progress for several years in cooperation with the Research Committee of the American Association of Textile Chemists and Colorists. Results of some fading tests made under controlled conditions of humidity and temperature in an apparatus devised at the bureau in which a 1000-watt incandescent lamp is used as a light source have been reported.' Extensive sun and daylight exposure tests as well as artificial light exposures have been in progress this summer. Duplicate sets of about twelve hundred samples each, representing the important cotton, wool, and silk dyes in two or three strengths and also some lake and pigment colors in printing inks, have been used. Progress has been made in this work and it is not too early to anticipate that standard methods acceptable to practically all concerned with dyes and dyed materials in this country will result. The European industry is taking an active interest in the standardization of fastness tests and international methods of test may eventually be established. The adoption of standard methods of test will lead directly to I
Vol. 18, No. 12
adequate tables of the fastness properties of dyes undar the different conditions of use. One of the objects of the dye laboratory has been active coKperation with other organizations and the industry. The work on fastness tests with the American Association of Textile Chemists and Colorists already mentioned, has brought the bureau into close contact with practical problems. The association has found it advantageous to employ a research assistant for its work in the dye laboratory this summer. A research associate from the Climax Molybdenum Company has studied the use of molybdenum compounds in the preparation of color lakes under the supervision of the dye laboratory. Dye problems arising in other government departments, such as the Army, Navy, Commission of Fine Arts, and Federal Specifications Board, are often referred to the d y e laboratory. Future Development
The limited personnel of the dye laboratory, its equipment, and the apparent requirements of the industry led to t h e restriction of the work, for the first few years a t least, to problems of application. It is hoped that interest in the possibilities for constructive work and the peculiar advantages obtaining at the bureau will create a demand for the expansion of the laboratory in other directions. Perhaps this can best be accomplished by the appointment of research associates paid by the industry for the study of specific problems. Bibliography 1-Gibson, McNicholas, Tyndall, Frehafer, and Mathewson, Bur, Standards, Sci. Pafier 440 (1922). 2-Appel, A m . Dyestuf Rept., 13, 507 (1924). 3-Appel and Brode, I n d . Eng. Chem., 16, 797 (1924). A m . Dyestuf R e p f . , 14, 882 (1925). 4-Appel, b B r o d e , J . Phys. Chem., S O , 56 (1926). 6-Appel, Brode, and Welch, I n d . Eng. Chem., 18, 627 (1926). 7-Brode, J . A m . Chem. SOC.,48, 1984 (1926). 8-Brode, Znd. Eng Chem., 18, 708 (1926). J . A m . Chem. Soc., 48, 1877 (1926). g-Brode, l0-Stmdard spectrophotometric measurements on certain textile dyes will be published in the nedr future. 11-Spectrophotometric work on methyl and dimethyl substituted benzeneazophenol will appear in J . A m . Chem. SOC.
Fur-Dyeing and Fur Dyes in America By William E. Austin STEINFUR DYEINGCo., INC., N E W YORE, N. Y.
T
HE consideration of fur-dyeing at this time is apropos
because it is essentially dye production, only the coloring matter is produced directly on the fiber. With the exception of a few dyes of vegetable and mineral origins, fur dyes are certain types of coal-tar intermediates which on oxidation yield insoluble, co!ored substances, for example, aniline black. History of Industry
Fur-dyeing is not a new industry in America. In fact, there were fur-dyeing establishments here over one hundred years ago, and prior to 1915 there were about fifteen firms engaged in the dyeing of furs, mainly in and about New York. The domestic output, however, was quite insignificant as compared with the consumption, a situation analogous to the position of the coal-tar dye industry in this country at that time. About 90 per cent of the dyed furs worn here
before 1915 bore the stamps of foreign dyers, chiefly German,. in spite of the fact that most of these furs came originally from North America. Purchasers of dyed furs were accustomed to ask for the Leipzig dye, this being considered universally the standard of quality. The small percentage of furs which were dyed here were produced with the aid of German dyes, as none of the coloring matters were made here. About half a dozen different dyes comprised the selection from which the dyers made up their various dye solutions, and these dyes were p-phenylenediamine, p-amidophenol, o amidophenol, m-phenylenediamine, m-toluylenediamine, and aniline salts. From these were obtained black, brown, and gray shades, reproducing or imitating the natural colors of animals. The application of the dyes was limited to comparatively few classes of furs, following along the traditional lines as practiced ... abroad.
