NECESSITY OF FUME HOODS FOR HIGH-SCHOOL LABORATORIES
A study of sixteen high-school chemistry laboratory manuals, including 1960 experiments, reveals that there are only 102, or 5.2per cent., of the exercises that require the use of fume hoods. These results would seem to indicate that the installation of expensive fume hoods for high-school use i s highly questionable. However, obnoxious and poisonous gases should never be allowed to circulate freely i n any laboratory or school building. Suggestions are given for controlling and absorbing the excess of each of the gases involved. .
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The installation of efficient fume hoods with forced ventilation involves considerable expense. Many so-called fume hoods as found in many highschool chemistry laboratories are little more than holes in or boxes along the wall, possibly connected with the outside air by a vent, and sometimes even connected to the outside by an opening leading upward for several feet or even stories to the roof of the building. When it is remembered that ammonia and carbon monoxide are practically the only obnoxious gases lighter than air that are ordinarily generated by high-school students in the regular course of their laboratory work, the futility of such fume hoods will be immediately obvious. In addition mazy high-school chemistry instmctors apparently think that fume hoods are anjndispensable adjunct to their laboratories. The authors are perfectly willing to admit that fume hoods are desirable, especially where finances, wall spa$e, and other conditions will permit the installation and use of efficient hoods with forced ventilation. However, we are quite as unwilling to admit that they are absolutely necessary, at least until information is available as to the number and type of experiments that ordinarily require such fume hoods. For these reasons it seemed advisable to make a study of several representative highschool chemistry manuals to determine what gases that would ordinarily lie considered obnoxious are liberated in the laboratory. The percentage of the total number of experiments requiring fume hoods was also determined as well as how these gases might otherwise be conveniently handled in the laboratory by dissolving any excess in suitable solvents, or by meails of other types of ventilation. In making this study sixteen high-school chemistry laboratory manuals were surveyed. The gases which were considered obnoxious and were included in the final tabulation were chlorine, hydrogen sulfide, ammonia, hydrogen chloride, bromine, sulfur dioxide, carbon monoxide, and finally arsine, nitric acid, and sulfur trioxide in the case of one laboratory manual each where the conditions were such as to make this seem desirable. Any one familiar with any typical manual recognizes that many of the above 919
920
MAY.1932
JOURNAL OF CHEMICAL EDUCATION, Nama of Labmalory Manvol ond Author
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Laboratory Experiments in Chemistry-N. Henry Black Laboratory Manual to Accompany Foundations of Chemistry-Blanchard and Wade Laboratory Studies in Chemis--Robert H. Bradbury Experiments in the Chemistry of Common Thinp~Brownlee, et at. Labaratory Exercises to Accompany First Principles of Cbemistry-Brownlee, et al. Laboratory Manual for HighSchool Chemistry-George H. Bruce Experiments and Laboratory Exercises for Chemistry in EveryG. Cook day Lif-Charles Laboratory Manual of Chemistry-Ernest L. Dinsmore Laboratory Exercises in Chemis try--Charles E. Dull Applied Chemistry, A Laboratory Manual-Emery, Boyuton, and
Miller Laboratory Exercises for Essentials of Chemistry-Hessler and Smith A Laboratory and Note Book to Accompany Beginning Chemistry and Its U s e s I r w i n , Rivett, and Tatlock Laboratory Practice in Chemistry-McPherson and Henderson Experiments for General Chemistry-Lyman C. Newell Exercises in Everyday Chemistry-Alfred Vivian Laboratory Manual of Chemistry in the Hom-Henrv T. Weed 5 14 14 14 17 22 13 102 Total * Total includes one ex~erimenton nitric acid. **Total includes one experiment on arsine. t Total includes one experiment on sulfur trioxide
gases are frequently generated in extremely small amounts, usually in test tubes for one single test, and then the contents of the test tubes are im-
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FUME HOODS FOR HIGH-SCHOOL USE
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mediately emptied into the drain with a copious flow of water. The laboratory manuals do not recommend the use of fume hoods in such cases and few if any students or iustrnctors use the hoods for such tests, even if they are available. Obviously, tests where these gases are produced in such smaU quantities as not to be noticeably offensive or dangerous, mere not included in the tabulations. However, in all cases where a regular generator of 125 to 1000 cc. capacity or larger is used to generate any of the above gases for a general study of their properties or uses, this experiment was included in the results as published. On this basis the tabulated results on page 920 were obtained. The sixteen laboratory manuals are arranged in alphabetical order of the author or senior author without any other reference to results or conditions. I t is interesting to note that there are only 102 experiments out of the total of 1960 in which enough of any obnoxious gas is liberated to demand particular precautions to eliminate a probable excess. This constitutes only 5.2 per cent. of the total number. If all the 1960 experiments average about the same length and if these typical laboratory manuals are to be made the basis of the high-school student laboratory work, then these results would indicate that such fume hoods, even if available, would stand idle about 95 per cent. of the time. There are also many other methods by which these gases can be handled successfully in the laboratory without the use of fume hoods. Where chlorine is liberated the excess gas can be successfully dissolved in sodium hydroxide solution. Hydrogen sulfide can be dissolved in water or, better, in a concentrated solution of sodium or potassiudi hydroxide. Ammonia can be successfully dissolved in water or an acid such as sulfuric or nitric acid. Hydrogen chloride can be readily dissolved in water or a basic solution. Bromine will dissolve in potassium or sodium hydroxide solution. Sulfur dioxide will dissolve very nicely in water or again in a solution of sodium or potassium hydroxide. Excess carbon monoxide can be collected over water and later burned. By these simple methods the gases that are injurious will not be circulated inside the laboratory. Instead of having large generators for the production of these offensive gases in cases where they are very poisonous to the workers, the gases can be generated directly in small bottles where the tests are to be made and kept in them until used. This method has the advantage over the generator type in that there is little chance for the gas to escape through leaks in the tubes. For example, chlorine can easily be generated in a small 4-ounce gas bottle at room temperature by the action of about 1 or 2 cc. of concentrated hydrochloric acid on 5 g. of solid potassium chlorate. The bottle can be conveniently covered with a glass plate to prevent the escape of the gas. Many instructors deem it advisable to use teacher-demonstrations in performing those laboratory exercises where appreciable
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JOURNAL OF CHEMICAL EDUCATION
MAY. 1932
quantities of these offensive and poisonous gases are liberated. This has the advantage of one generator instead of one for each student or group in the laboratory. In addition the technic of the instructor should be superior to that of the students, thus eliminating much of the excess and unnecessary gas as well as customary leakage. If, after following these precautions, any gas should escape into the laboratory it can usually be driven from the room by throwing open a few windows. This study seems to reveal little if any justification for the purchase and installation of fume hoods for high-school laboratory work in chemistry if the courses offered are to be based upon any of these sixteen typical highschool manuals, especially if the cost of such hoods is excessive. Likewise, since all gases listed except ammonia and carbon monoxide are heavier than air, some system of forced ventilation should be provided if such hoods can be procured with the finances available and are to operate efficiently. In many modem laboratories i t is customary to ventilate the entire room through the hood. In such cases where forced ventilation is provided, the added cost of some hoods would be confined largely to the hood itself. Frequently hoods are bnilt in hollow walls, these walls also carrying the other service lines of the laboratory. However, the fact cannot be overestimated that if such hoods are not provided then every other precaution possible must be taken not to fill the laboratory or building with offensive and poisonous gases, thus endangering the comfort and health of the students in the chemistry classes or school. Perhaps forced ventilation in the entire building and especially in t$e chemistry laboratory may be a better solution for this problem.
