The NOSE in ihe CHEMISTRY LABORATORY LEONARD A. FORD1 Sioux Falls College, Sioux Falls, South Dakota
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ficatiou of laboratory odors involve the use of the sense of smell. The chemistry student uses the sense of sight when he sees experiments performed by himself or others, reads his book or review outlines, writes examinations, works problems, or sees diagrams on the board. He uses his sense of hearing when he listens to lectures, discussions, and reports. ~~ k i ~ The t~ ~nose ~ , is sensitive ~ - to incredibly small amounts of odorous materials and is probably more acute than the
HE most effective method of acquiring information on any subject is one which will permit the use of several senses. Those of us who study chemistry are fortunate in that we can use the sense of touch and smell as well as sight and sound. The sense of touch is developed in the manipulation of laboratorv a ~ ~ a r a t u sThe . discrimination and identi-
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TABLE 1
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Bmmine Chlorine ladine H y d r m h l d e acid Nittie acid Acetic acid Benzene Ethyl alcohol Ether Gasoline Naphthalene Phenol Formaldehyde ~itrobenzene Carboo dirulfide Ammonium hydroxide Pyridine Hydrogen sulfide Oil of wintergreen Oil of cinnamon Amyl acetate Ethyl beoroate Chloroform paraldehyde
3 0 3 2 3 1 2 1 8 1 1 1 0 1 40 2 6 30 1 9 1 30 1 1 4 3 3
1 4
1
1
2
1
1
1
1
1
1
1 1
1
1
1
1
42 1
34
2 36
1 42
1 1
1
1
1
1
3
1 1
3
1
2
2
1 37
1
35 3 4 2
2
1
1
1
42
1 1 1
2
1
1
3
1
1 30
1 1
32
1
1 1
3 2
38 43 43 43 42
1
1
42 1 1
1
1 2 1
other senses. It is estimated that 2 X lo-" milligrams or two hundred million molecules of mercaptan will stimulate the sense of smell. Many experiments in organic as well as inorganic chemistry involve materials with decided odors. Yet laboratory manuds and textbooks seldom refer to odors except to describe them as being "like rotten eggs," "pungent," "characteristic," "sharp," "offensive," "sufTocating," "irritating," or "like rotten horseradish." In discussing the physical properties of elements or compounds mention is usually made of physical state, density, solubility, melting and freezing points, color, but rarely taste and odor. Odor or the lack of it is as characteristic a property of matter as is color or the lack of it. The eye is sensitive to slight changes in color. May we not expect the nose to be likewise sensitive to slight changes in odors? An investigation of student response to odors would show if there were any value in placing more emphasis on this phase of the laboratory work. Do students recall odors? What is the explanation for inability to discriminate between odors? Among which odors is there the greatest amount of confusion? In an attempt to answer these questions an investigation of odorous substances was carried out with forty-three beginning students in chemistry. Twenty-four small labeled bottles containing known odorous substances in the form of solids, liquids, and dissolved gases were given to each student to study and compare by means of cautious sniffing. On a mimeographed sheet containing the names of each substance the student recorded any descriptive words that came to his mind upon sniffing the substance. Approximately five hours were given to this study which should enable the student to associate name and odor to a fair degree. The student was then given the same
1
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3 1
1
2
4
2
5 27
2 2
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twenty-four substances in the form of unknowns. Each bottle was covered with a paper jacket to prevent identification by appearance. An assistant held the bottle while the student sniffed the odor. The most likely name of the unknown substance was written on a slip of paper by the student who was permitted to consult his previously prepared mimeographed sheet containing descriptions. of odors. This procedure was followed with each bottle in one-minute intervals. The results are recorded in Tahle 1. The horizontal column contains the names of the unknown substances given to the students. The vertical column contains names assigned to them by the students. An example to illustrate the u s e d the table is given: Ammonium hydroxide is called hJidrochloric acid three times, formaldehyde twice, and ammonium hydroxide thirty-eight times. The substances are arranged in order of ease of identification in Tahle 2. TABLE 2 Pyridine Hydrogen mlfide Oil of wintergreen Oil of cinnamon Amyl acetate Bewene Iodine Ammonium hydroxide Phenol Ether Farmaldehyde Ethyl alcohol Ethyl benzoate Carbon dirulfide Acetic acid Nitrobenzene Bromine H y d r m h l d e aeid Nitric acid Chloroform Paraldehyde Chlorine
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The compounds in the upper part of the series in Table 2 are probably true odors as distinguished from
the others which are irritants. The following excerpt is quoted from the Encyclopedia Britannica (Vol. 20, page819,14th Edition) under the heading "Two kindsof Response" to show that a difference exists between those substances called imtants and true odors. "The lower portion of the nasal chamber is respiratory, and .only its uppermost part is olfactory. Nevertheless, the whole surface of the chamber is in a way sensitive, for the fifth or trigeminal nerve is distributed throughout it. This nerve, once supposed to have t o do with smell, is now definitely known to be concerned with irritants. If the olfactory nerve in a dog is destroyed, the animal will still sneeze when vapor of ammonia enters its nostrils. The same is true of human beings who through disease have lost the olfactory nerve but who still retain the trigeminal nerve. Many persons who fail to recognize the mare delicate odors of flowers, food, and the like are nevertheless readily cognizant of even minute quantities of chlorine, ammonia, and other like substances. These materials are not odorous materials in the proper sense of the word but are irritants and affect the terminals of the fifth nerve, not those of the first nerve. True smell has to do with relatively delicate perfumes and odors and is mediated by the first nerve in contrast with initants which stimulate the fifth nerve. I t is of considerable importance in the study of olfaction t o distinguish between these two nervous activities."
In an attempt to explain why some substances are
more readily confused with others, it is well to point out that a difference exists between those substances that are nasal irritants and the true odors. The acidic substances hydrochloric, nitric, and acetic acids and the halogens were confused among themselves and were among the most difficult materials to identify. These substances have an irritating effect on the nose. It is interesting to note that there is a marked difference in ease of identification of the halogens, the order being: iodine, bromine, and chlorine. The first six substances in Table 2 were identified correctly by practically every one. The.se materials are true odors. Five students were correct in all instances. The average number of mistakes in identification made by each was five. This reveals that students can correlate the identity of odors and substances to a rather high degree and that odors have a distinct memory "due, A number of the compounds studied were unfamiliar, and i t was necessary to learn new names as well as association between name and odor. A greatly extended period of study and comparison of odors beyond five hours would probably show better results.
