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ISDUSTRIAL A S D ENGINEERISG CHEMISTRY
ture. By this time the reaction mixture had set to a semi-solid mass of aniline sulfate and the fortified acid. The mixture was then distilled by sinking the flask in water at 70” C. while maintaining a vacuum of 60 to 65 mm. in the system. The receiver consisted of two flasks in series, each surrounded by chipped ice. In this way 95 grams of a colorless liquid was obtained. 9 test for the presence of sulfuric acid by means of barium chloride solution was negative. Titration of a weighed sample with standard sodium hydroxide solution proved it to contain 99.1 per cent formic acid (melting point, 6.0” C.). Recovery was approximately 90 per cent calculated on the total amount of formic acid introduced into the system. The water flowing from the aspirator in the final distillation was slight’ly acid to litmus; therefore, the recovery would have been higher if all traces of acid could be condensed. .1 small amount of oil (approximately 3 grams) came over when the aniline-formic acid mixture was dist,illed to produce formanilide. It could not be crystallized and probably con-
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sisted of a mixture of aniline and formanilide. I t was saved and thrown in with the aniline sulfate when the latter was converted to aniline.
Literature Cited -Uexejeff, IT., Ber., 10, 708 (1877). Gasiorowski, K., a n d Merz, T’., I h i d . , 18, 1001 (1885). Gerhardt, Ann., 60, 311 (1846). Tobias, G., Ber., 15, 2443 (1882). Lllmann, “EnzyklopRdie der technischen Chemie,” 2nd ed., T’ol. I, pp. 342-3, Berlin a n d Vienna, Urban & Schwartzenberg (1928). (6) Wallach, O., a n d W‘iisten, M., Ber., 16, 145 (1883). (1) (2) (3) (4) (5)
RECEIVED March 20, 1933. Presented before the Division of Industrial and Engineering Chemistry at the 89th Meeting of the American Chemical Society, New York. N. Y., April 22 t o 26, 1933.
Seeking a Working Language for Odors and Flavors E. C. CROCKER Arthur D. Little, Inc., Cambridge, Mass.
A
IXSTRUJIEST that can detect a millionth of a milligram, and in some cases less than a billionth of a milligram, of the vapor of hundreds of kinds of organic substances should inspire our admiration. That instrument, with its spectroscopic sensitivity and great convenience of operation, is the human nose. Difficulties of experimentation have tended t o make investigators avoid working on smell and smelling, so that today entirely too little is known concerning them. There should be both commercial and scientific value in a better understanding of the nature of odor and of the mechanism of smelling, as well as in an adequate, logically founded language for odor description. It does not take much argument to convince an organic chemist that his sense of smell is of great value in his work. But very few chemists, without a careful appraisal of the matter, give this lowly and despised sense even a portion of its proper credit. By its means, for example, leakages, toxic vapors, or fires may usually be discovered in time for action leading to safety. A sniff of the vapor when the stopper is removed from a bottle gives assurance that the label is correct, K i t h a deeper and more searching type of smelling, supplemented by judicious tasting, the food chemist judges the quality and even the history of a questioned article of food. The perfume chemist goes still further in his nasal analysis, and to meet his approval a natural or synthetic material must either be very pure or skillfully disguised. During the past few years the public has become increasingly more odor-conscious and is gradually demanding a perfection in the odors of consumer goods comparable with the great improvements that have recently taken place in their physical qualities and appearance. Whatever commercial products cannot be made strictly odorless must a t least be made to smell pleasantly. Several perfume material houses are now specializing in producing odorizing or deodorizing S
compoqitions for a wide range of industrial and consumer products including rubber, linoleum, paints, inks, paper, and oils. “Sell-by-smell” is becoming a potent sales consideration. In spite of the importance of odor, industrially as well as esthetically, there is no competent, universally accepted method for its characterization. The odor descriptions given in chemical handbooks are pitifully inadequate. To find the odor of a chemical described as peculiar, nauseating, foul, characteristic, or pleasant, gives but a trace of the help reasonably expected. Such rough comparisons as spicy, tarry, anisic, musty, or aromatic a t least specify the class, even though much more information is usually desirable, especially where an odor may have the qualities of several such classes simultaneously, only one of which is mentioned. Among perfumers the situation is not so helpless, for a rigid nasal
The human nose is a detecting agent of extraordinary sensitivity, giving indications in some instances with less than a billionth of a milligram of material, in vapor form. It is very convenient to apply for analytical or comparative purposes, yet its actual usefulness is seriously limited by lack of an adequate language for expression and especially for record. Chemists are little helped by the customary textbook descriptions of odor as “peculiar,” “characteristic,” etc. This article summarizes what is now known about odor and the sense of smell, draws analogies from work on the other senses as to what may be expected of accomplishment, and makes a strong plea for more workers of various types to develop an adequate method of odor expression.
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education and discipline are required in the business. Memorizing the odors of all the ordinary flowers, fruits, and even animals, as well as of vast numbers of pure chemicals, gives a rich background against which the odor in question is projected and compared. With both chemists and perfumers, however, the description of odors is inadequate and does not even approach the exactness possible with the senses of sound and sight. An analytical system of odor classification is particularly needed to define odors in such a manner that attention can be paid to the expression of even slight differences. The foundation of such a system should not require the accurate memorizing of large numbers of distinctive odors; rather it should be sufficient to learn a few elemental types, as the colors are learned in sight, or the tones in sound. When that is done for, the pure sense of smell, it will apply automatically to flavor, which is odor plus taste.
Smell and the Other Senses I n the case of the sense of taste it is possible to excite the actual taste buds on the tongue with various solutions to find the fundamental types of stimuli, such as sour, sweet, salty (IO), or bitter. Kot so the sense of smell. The sensitive zone (8) is no larger in area than two finger nails and is located inaccessibly high in the nose, just beneath and behind the eyes; this place is particularly difficult of access for experimentation. Perhaps the most important point, however, is that the sense of smell is difficult to work with in all ways, and is not a problem for anyone t o attack without plenty of time and willingness to work. The experimenter who should have the best chance to find out most about the smelling area itself would be primarily a physiologist, with considerable acquaintance with chemistry, electricity, psychology, and other branches of science. There have been whispers in the literature that odorous vapors affect the electrical conductivity of air and hence may be recordable by means of an electroscope or through the medium of an electron tube, but the writer has not been able to find any effect whatsoever of this kind, even in the case of powerful odors. The quantities dealt with are exceedingly small, so that instrumental detection of any kind of “electric nose” seems a t present practically out of the question. Physiologists have made notable advances (6) during the past five years in understanding the nature and means of transmission of the sense of sound, or hearing, by studying electric “action currents.” They have proved, for instance, that sound impressions are transmitted from the ear to the brain by electric currents in the nerves. They have “tapped the wires” of the auditory nerve of a cat by suitable electrodes and have led out the feeble action currents, amplified them, and made them operate a loud speaker. Words spoken to the cat’s ear have been reproduced faithfully by the loudspeaker, even though the cat was under deep anesthesia, just so long as its heart was still beating or had not been stopped for much more than an hour. It is conceivable that this technic, which works so admirably with hearing-a relatively simple sense and apparently only a specialization of the sense of touch-may also be able to give much information about the sense of smell. But before that is possible, many difficulties will have to be overcome. Work on the allied sense of taste, which is the more convenient, should properly come first. To analyze the sense of taste, it may be necessary to find ways to amplify the action currents of single nerve fibers to make the indications intelligible. If the electrical impulses of the entire sense of taste were to be fed into a loud-speaker, the sound might be a roar, or if registered on an oscillograph, a wave. Very detailed indications are wanted. They are far from being realized even for the sense of taste, but are by no means unthinkable. For-
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tunately, animal experimentation is possible, and the animal does not need to be conscious during the work. Even the lower animals, such as fish, may prove suitable subjects for preliminary study. I n tasting, very small quantities (4) of certain chemicals produce distinct impressions, but the quantities required for minimum taste perception are gross compared with those for smell perception. From 1-cc. sips, one can just detect the sweetness of 0.7 per cent cane sugar solutions. Thus the taste threshold for sugar is about 7 mg. The lower limit for salt is about 1.5 mg., and for tartaric and other acids is of the order of 0.2 mg. Passing to materials of the strongest taste, the limit for caffeine is 0.04 mg., for quinine 0.016 mg., and for saccharine 0.012 mg. Roughly, the limit for a taste of the most powerful stimulus known is not far from 0.01 mg. About 100 cc. of air must be sniffed for ordinary odor discernment, although half this amount will register if the odor is strong. Fair (6) quotes detectable concentrations in air for some of the most odorous chemicals in milligrams per liter: Chlorophenol Ionone Artificial musk Vanillin
0.000 004
0 ood 000 1 to 0 000 000 05 0~000’000’04t o 0.OOb OOb 005 0.000:000:5 to 0.000,600,600,2
If 0.000,000,000,1mg. per liter is taken as the ultimate in dilution which is perceptible, the amount per sniff is of the order of 0.000,000,000,01 mg. The sense of smell is thus many million times more delicate than the sense of taste. However, smelling does not approach single-molecule sensitivity, for in 0 000,000,000,01 mg. of vanillin there are 4 x 107 or 40,000,000 molecules. If only 1 molecule in 1000 of those sniffed falls on the sensitive area, some thousands are necessary to give a smell impression, even with this most actively odorous agent. Taste is virtually a contact sense, since considerable substance must be applied to excite the nerves. By contrast, smelling is a sense operable a t a distance, because exceedingly small amounts of matter are sufficient for distinct perception. From all practical considerations, it seems that our objective information on the sense of smell will be preceded by similar information obtained on the sense of taste. The sense of smell is exceedingly delicate, ordinarily responding to amounts of material of the order of thousandths, or even millionths of a milligram, of apparently inert matter. There seems little present opportunity to deal with such minute amounts objectively, by means of instruments, even of great sensitivity. We are, therefore] forced for the present to study the matter subjectively, by analyzing the impressions produced by odorous materials on the nerves and on the mind of the human subject. It has been observed that many odorous materials are easily susceptible t o oxidation. There is the remote possibility that an oxidation cell could be devised to detect very small amounts of oxidizable materials. Such a device might take on some of the functions of the human nose, as the quinhydrone electrode takes on a t least part of the sournessdetecting function of the human tongue. But since such oxidation cells are apparently not yet invented, that possibility must be heavily discounted, and reliance be given to the subjective method of approach.
Odor Analysis It is now generally accepted that the nose perceives other impressions, especially that of pain, besides those of pure odor, just as the ear or the eye feels pain when the sound or light is of excessive intensity. Pain in the nose is called pungency and is apparently the same sensation whether caused by the vapors of such chemically different substances as strong ammonia, formaldehyde, or acetic acid. When
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INDUSTRIAL AKD ENGINEERING CHEMISTRY
these substances are greatly diluted, their pure odors, apart from pungency, may be perceived. Menthol feels cool when applied to the skin of the forehead. It gives the same sensation when smelled or tasted. Thus there are cold-impression nerves scattered over the body including the inside of the mouth and nose, though possibly not on the actual smell area in the nose. It is the true smell sense that’operates when the vapor is highly diluted in which we are principally interested. Zwaardemaker (11), forty years ago, grouped all odors into nine general classes, most of which he further subdivided. For convenience of reference, Bogert’s arrangement of this system is given ( 2 ): 1. Ethereal or fruity; characteristic in general of fruits, and due in most cases to the presence of various esters; includes also beeswax and certain ethers, aldehydes, and ketones. 2. Aromatic: a. Camphoraceous : borneol, camphor, eucalyptole. b. Spicy: eugenol, ginger, pepper, cinnamon, cassia, mace. c. Anise-lavender : anethole, lavender, menthol, thymol, safrole, peppermint. d. Lemon-rose: geraniol, citral, linalyl acet’ate,sandalwood. e. Amygdalin: benzaldehyde, oil of bitter almonds, nitrobenzene, prussic acid, salicylaldehyde. 3. Fragrant or balsamic: a. Floral : jasmine, ylang-ylang, orange blossoms, lilac, terpineol, lily of the valley. b. Lily: lily, tuberose, narcissus, hyacinth; orris, violet, ionone, mignonette. c. Balsamic: vanillin, piperonal, coumarin, balsams of Peru and Tolu. 4. Ambrosial: musk and amber. This odor is present in the flesh, blood, and excreta (referable to the bile) of certain animals. 5. Alliaceous or garlic: onion, garlic, and many compounds of sulfur, selenium, tellurium, and arsenic: a. Alliaceous: hydrides of sulfur, selenium, and tellurium, mercaptans, organic sulfides, thioacetone, asafetida. b. Cacodyl-fish odors : hydrides of phosphorus and arsenic, cacodyl compounds, trimethylamine. c. Bromine odors: bromine, chlorine, quinone. 6 . Empyreumatic or burnt: as in tar, baked bread, roasted coffee, tobacco, benzene, naphthalene, phenol, and products of the dry distillation of wood. 7. Hircine or goat: due in the case of this animal to the caproic and caprylic esters contained in the sweat, and typified also by perspiration and cheese. 8. Repulsive: such as are given off by many of the narcotic plants and by acanthus. 9. Nauseating or fetid: such as are given off by products of putrefaction (feces, etc.), and by certain plants.
Henning ( 7 ) sought to analyze the sensation of smell into its fundamentals, and arrived at the conclusion that there are six types of odors: 1. Spicy, notable in cloves, cinnamon, nutmeg, etc.
2. Flowery, notable in heliotrope, jasmine, etc. 3. Fruity, notable in apple, orange oil, vinegar, etc.
4. Resinous, notable in coniferous oils and turpentine. 5. Foul, notable in hydrogen sulfide and products of decay. 6. Burnt, notable in tarry and scorched substances.
H e sought to limit all odors to combinations of these six, represented, for convenience, along the edges or on the surfaces of a triangular prism, with the pure abstract sensations at the points. This was later reduced to four fundamental sensations by the present writer and his co-worker Henderson ( 3 ) : 1. Fragant or sweet, corresponding to Henning’s blumig or duftig. 2. Acid or sour, not previously characterized. 3. Burnt or empyreumatic, like Henning’s brenzlich. 4. Caprylic or oenanthic, prominent in the Odores Hircina’ of
Linnaeus and the Kaprylgeruche of Zwaardemaker.
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Besides reduction of the number of apparent fundamentals, the present workers devised a semi-quantitative numerical arrangement whereby any odor may be expressed as a fourdigit number-for instance, 3803 for acetic acid, 8445 for benzyl acetate, or 6323 for cY-terpineol-where the successive figuresare for the four types, fragrant, acid, burnt, and caprylic, in succession, on the basis of 8 for most powerful and 1 for just detectable. It has been pointed out that this numerical system is apparently a n application of the Weber-Fechner psychophysical relationship, which states that sensation varies arithmetically as intensity varies geometrically. If two successive digits correspond to an intensity range of 2:1, then for eight detectable degrees of sensation difference there should be 2* or 256 fold range of intensity. At each step an intensity ratio of greater than 2 : l is probably involved, so that the actual intensity range for the eight digits is correspondingly greater.
What Is Needed? Possibly no one of the above sydems of clabsification 12 adequate or even fundamentally correct; yet there is little in the literature to indicate that the subject has been given a great deal of thought. It is indeed regrettable that psychologists have not been more active and searching in studying this subject which is within their field, and which is surely not too difficult to test. There is, for instance, the attractive chance of securing valuable data from subjects who may have only a partial smell sense. The physiologist should be able to contribute most to the objectivity of smell. For instance, he should be able to differentiate the several types of nerves in the smelling area, as has been done for feeling (9) and for taste. This should throw real light a t least on the number of fundamental types of odor perception that exist, which is still uncertain. The newer electrical nerve technic may be able to discover different kinds of impulses from the different nerve types. The organic chemist (1) may well continue his attempts t o correlate odor type and chemical structure, as has been done so successfully for dyes and so assiduously for medicaments. It is more than accidental that 1,3,4-benzene derivatives tend to be highly odorous. Of disubstituted benzene compounds, the meta isomers usually have by far the least odor. The configuration of the molecule as well as the actual atoms and groups in its composition affect not only the intensity but also the type of odor. The rules, however, are not too well known. Just now the structural chemist working on odor 2s.constitution seems inclined to wait until the language and definition of odors are better before he contribute5 much more-a paralyzing situation. Possibly the finest work of all could be done in this really difficult field by a sizable research group with a wide range of training and technic. This group should be able to devise a system of practical utility, best of all if based on experimentally determined physiological entities. With enough workers, interesting and important findings are virtually certain. The chief value of a better system of odor analysis and classification will be the basis it will provide for a real language of odor. Odor impressions are now entirely too personal, and terms are not in general use which can convey odor impressions accurately from person to person, verbally or by written record. With the attainment of such a system will come more odor-consciousness and accuracy. KO longer will the unknown odor be automatically treated as suspicious or unpleasant, but will be describable for what it is. It is not too much to look forward to a dictionary of odors wherein one may find the name to go with each complete impression and a list of the substances which have that type of odor. The
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practical value of improved understanding of odor will apply equally to what we call odor, and to that complex of odor and taste that we call flavor.
Literature Cited (1) Bogert, Am. Perfumer, 24, 15, 235, 357 (1929). (2) Bogert, J. IND.ENO.CHEM.,14, 359 (1922). (3) Crooker and Henderson, Am. Perfumer, 22, 325 (1927). (4) Ibid., 27, 156 (1932). (5) Davis, Handbook of General Experimental Psychology, p. 962, Clark University, 1934.
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(6) Fair, Haward Eng. School, P u b . 108 (1934); Am. P e - f i m z e r , 28, 573 (1934). (7) Henning, “Der Geruch,” Leipzig, 1924. (8) Parker, “Smell, Taste, and Allied Senses in the Vertebratee.” p. 23, Philadelphia, J. B. Lippincott Co., 1922. (9) Ranson, Science, 78, 395 (1933). (10) Renshaw, Ibid., 80 (Suppl.), 8 (1934). (11) Zwaardemaker, “Die Physiologie des Geruchs,” Leipzig, 1S95.
.
RECEIVEDM a y 6, 1935. Presemed before the Division of .igricultural and Food Chemistry at the 89th .Meeting of the American Chemical Society, S e w York, N.Y., April 22 to 26, 1935.
Cation Exchange Capacity of Activated Sludge .L. R. SETTER, G. RI. RIDEXOUR,
Activated sludge produced under normal operating conditions was used to study the cation exchange capacity as a measure of the colloidal property of the floc. It was found, that under conditions of sufficient oxygen tension and good purification, (1) activated sludge exhibits the colloidal property of having exchangeable cations, (2) the magnitude of exchangeable cations is similar to clays of high silica sesquioxide ratio such as bentonite, and (3) the settling character of the sludge improves with an increase in the cation exchange capacity and with a decrease in the total fat and fatty acid content.
HE activated sludge process can be coiiveniently subdivided into two separate and distinct parts; each part possesses definite functions: 1. The adsorption of sewage colloids and organic electrolytes by an “active” sewage floc or a returned, aerobically “humified” floc. 2. The stabilization of the freshly adsorbed material caused by partial, aerobic microbiological decomposition, resulting in the regeneration of the floc.
The first function occurs almost immediately whereas the second requires a longer time. The mechanism of the first function, that of adsorption or coagulation, has been described by various authors as being physical, chemical, and electrical in nature, with only vague explanat’ions as to what is meant. The purpose of this paper is to present a more clearly defined picture of the mechanism whereby sewage colloids are
AND
C. 3. HENDERSON
New Jersey Agricultural Station, New Bruiiswick, N. J
removed by activated sludge floc, and to show that variations in the colloidal properties of the active floc as determined by the cation exchange capacity are reflected in the composition and settling character of the floc. In several papers Mattson and his collaborators (1, 2 , 3, 8) have shown that soil clays, soil organic complexes, and laboratory-prepared colloids are amphoteric in nature; that they possess colloidal properties by virtue of the dissociation of ions; and that these ions may be displaced by exchange reaction with less dissociated ions of like charge. Recently Smith (9) found that various alkaloids could be removed by neutral bentonite. The soluble or dissociated cations of the bentonite were replaced by the alkaloid cation through the amine linkage. Similar evidence by numerou? investigators leads us to the assumption that the activated h d g e matrix also has both acidoid and basoid propertie. by virtue of dissociated ions which will be displaced by lesq di-qociated sewage colloidal ions. To substantiate this assumption, samples were collected every two weeks for one year from a New Jersey activated Yludge plant operating under normal conditions of purification. Daily operating and chemical control records were available over the entire period of study. The determination of cation exchange capacity and total fats and fatty acid4 on these samples, along with the purification and settling indices, were used to determine the effect of fats, fatty acids, and cation exchange capacity of the activated sludge floc on It. settling and compacting characteristics. These same determinations mere also correlated with the sexage purification resultq.
JIethods Wherever possible official methods were used; new and modified methods were briefly as follows :
