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JOURNAL OF CHEMICAL EDUCATION
SEMIMICRO TECHNIQUES FOR HIGH SCHOOLS FOSTER H. HOFF' and ALFRED S. BROWN Colgate University, Hamilton, New York
TAE success of the semimicro technique in the field technique, since a great variety of experiments may be of qualitative analysis has led to its consideration in the formulated once the major operations are specified. field of general chemistry, teachers interested in the Secondly, web have asked "a number of high-school problem of laboratory work in high schools having been teachers to consider the possibility of using the semiprominent in this exten~ion.~-~ Previous studies con- micro technique in their laboratories and to list quescerning the value of the semimicro technique for the tions which they care to ask in connection with the high-school chemistry laboratory have stressed results change from macro to semimicro techniques. We have obtained in specific laboratories. As a consequence attempted to correlate these questions, to answer them, the average high-school teacher has rgany unanswered and to present these answers to the teachers for their questions concerning the advisability of his using the appraisal. It is believed that the questions which semimicro technique. have been raised will be representative of those arising This study has attempted to bring two new ap- in the minds of many high-school teachers. proaches to the attention of high-school science teachOPERATIONAL ANALYSIS ers to help them reach a decision concerning the advisability of revising their laboratory method. It has The major operations of the general chemistry seemed important to prepare an operational analysis labbratory have been listed in Table 1. The table comparing the semimicro technique with the macro entries state the situations where the semimicro technique differs from the macro technique as a change in This material was taken from a thesis presented in parthl the size of equipment; as a change where the normal fulfillment of the requirements for the degree of Master of Arts procedure is modified; and finally as a change in which in Science Education. an entirely different procedure is introduced. It will WEISBRUSH, F. T., School Sci. and Math., 46, 768 (1946). WEISBRUSH,F. T., "Semi-Micro Laboratmy Exercises in be noted that in the semimicro technique most bperaHigh School," D. C. Heath and Company, Boston, 1942. tions are so closely related to those of the macro method 'LAWRENCE. SISTERMARY.AND W. J. SCMLLER. J. C ~ M .that the changes need not be alarming either for the ,~ EDUC.,18, 543'(1941). SCHILLEB, W. J., ET AL., "Chemistv Laboratory and Work- student or for the teacher. At the same time the semibook, Semi-Micro Methods," Globe Book Company, New York, micro technique offers several interesting alternate operations which enhance the value of the laboratory 1945. ~
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TABLE 1 Comparative Operational Analysis Zaboratmv- oneratia . 1. Weighing 2. Measuring volume 3. Heating 4. Distilline Evaporah Filtration Washing Grts generation Transfer of material Recrystdlisation Dissolving solids
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A simple redvetion in scale
A modified vrocedure
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An entirely difwent urocedure
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paratus will acquaint the student very readily with the effect of various filters since he may use cotton, glass wool, or synthetic fibers of the types used in commercial filter cloths, and may use filter aids in addition. Gas Generation. Semimicro equipment is readily used for standard procedures in the generation of such gases as hydrogen, oxygen, carbon dioxide, and the halogens. In addition, semimicro Kipp generators may be purchased or made for the generation of hydrogen sulfide, or this gas may be conveniently generated by heating a, mixture of sulfur and paraffin made porous with asbestos. HIGH-SCHOOL TEACHERS' QUESTIONS
Total
Chemistry teachers in a number of representative schools in central New York State were interviewed in work to the student. It may be helpful to list points connection with this problem. At the initial interview of significant differ~ncein the semimicro and macro each teacher was given the operational analysis substbtially as presented above and a brief summary of procedures. Measurement uJ Weight. The semimicro technique our tentative opinions. These served as the basis for requires scales sensitive to 0.01 gram. These are not the interview and the teacher was asked to criticize, expensive and are probably used in many high schools. to comment in any generally pertinent manner, and to Measurement of Volume. It is not necessary to use raise any questions which came to his mind a t the time. graduated cylinders larger than the 10-ml. size. More These questions, collected and combined, are presented interestingly, the volume of a reagent is conveniently in Table 2 below. Initial answers were submitted to measured by counting drops, and the student discovers the factors which determine the size of a drop. TABLE 2 Gas volumes are measured by displacement in the Problems of t h e Semimicro Method Anticipated bv same manner as in the macro procedures. It is sugTeachers gested that the student will have an opportunity to -~ use the weight of the displaced water and its density in A general science teacher, instructing chemistry classes, determining gas volume, which of course increases the would hesitate to make such an important change. Experiments might not be as vivid or perhaps as well seen. precision of the measurement of this quantity. The change from semimicro f o macro equipment in later Heating. While many sources recommend semimicro courses would be quite dificult. burners it has been the experience a t Colgate University Many of the educational problems of the macro method are eliminated by ra well-run macro laboratory. that ordinary Bunsen burners are satisfactory. Since A student derives manv benefits from handline chemicals in small quantities are heated (5-ml. test tubes, 10-ml. normal amounts. Erlenmeyer flasks, #OOO crucibles, semimicro casseroles, Administrative and Disciplinary Problem etc.) the time consumed in attaining required high Contamination might result from confusing covers on screw temperatures (and, for that .matter, in cooling) is cap bottles of the reagent kit, or hy contact of the pipet with other chemicsls on Gsttube walk and then replacing the reduced. v pipet in its dropping bottle. Evaporations are performed very readily in semi- 7. A bottle-filling problem might exist if the same reagent kits micro equipment and it should be quite practical to are nsed in more than one class. 8. The pipets in the dropping bottles might be used as s variabring each student into contact with both standard tion if the xmtcr pistol. laboratory evaporation techniques and the more Economic Problems modern use of heating lamps. The smaller size of the equipment makes it more fragile. 9. A hot-water bath, comprising merely a 250-ml. Miseellaneoua Problem beaker, is effective heating equipment in the semimicro 10. I t is difficultto change. technique. Often the authorities are unwilling to experiment a t 811. Filtration. The macro procedures normally are 11. 12. Cities in which more than one high school exists generally limited to the use of filter paper and funnels. Each of have standardized books and equipment so that one will hold no mecia1 advantaee over the others. these is available a t the semimicro scale and, in addition, the semimicro technique permits efficient use of centrifuges, which are comparatively inexpensive due interested teachers in a second conference and any to the size of the equipment involved. In addition, the additional points raised in this conference have been student can be readily introduced to pressure filtration by using the Barber filtration apparatus! This a p included in the following comments. 1. It is hoped that this study will make it easier for 0 BA~ER H., H., IWD T. I. TAYLOR, "Semi-Micro Qualitative a general science teacher to understand the questions which are raised a t the time of making the change from Analysis," Harper and Brothers, New York, 1942.' ~~~~
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macro to semimicro techniques. The advantages so far outweigh any known disadvantages that many teachers will feel compelled to make this change. 2. From the point of view of demonstrations it is obvious that the semimicro technique will be useless. We note that demonstrations before large groups require special apparatus and that this question is really not pertinent to the present discussion. It may be noted, however, that projection equipment has been devised for' demonstrating micro techniques.' The authors are of the opinion that students will benefit substantially if there is a reversal in the trend toward demonstrations as a substitute for individual laboratory work, and are further of the opinion that introduction of the semimicro technique will make this reversal eminently practical. 3. Lawrence and Schiller8 state that students who have had initial training in semimicro techniques seem fully capable of handling macro techniques in later courses. It has been our experience that students readily handle both semimicro and macro equipment interchangeably. From an educational point of view, it would seem that any such difficulty would mean that the student was acquiring additional experience. 4. Our response to the comment that many educational problems are eliminakd in a well-run laboratory using the macro technique is that it seems wise to use procedures which make it easier to organize a laboratory group effectively. The question of discipline frequently is related to the size of the group and we beiieve that larger groups can be handled with the semimicro technique while maintaining the high standard of discipline attained in a small group using the macro technique. 5. It is believed that the word "normal" here means simply traditional. We note that semimicro quantities probably approach the norms of professional work for physicians and nurses. It is obvious that the change from laboratory to tank-car quantities is so great that there is no significant differencein comparing the semimicro with the macro quantities'in this connection. Many industrial problems such as thesstudy of contaminants of a spotty nature require techniques of a high degree of refinement. We feel that an early introduction to the use of small quantities will he of benefit to future industrial technicians and scientists. We believe further that the semimicro technique offers definite advantages for those students who will have no further contact with scientific work either in school or in life in that i t develops keener powers of obsewation and a more critical evaluation of observations. 6. Trouble of course can always arise from an exchange of stoppers. The opportunity for this situation is enhanced considerably by the confusion which arises
' Dr. C. W. Mason of Cornell University has demonstrated micro techniques with special projection equipment heiore large audiences. This, however, requires very specialized equipment and training. LAWRENCE, SISTERMARY, AND W. J. SCHILLEX, Science Counselor, 2, 71 (1936).
from a group of students clustered around a few large reagent bottles. The semimicro technique contemplates approximately individual reagent kits for the chemicals frequently used. Our experience indicates that the decreased confusion results in much less exchange of bottle stoppers. The student selects the reagent bottle only a t the instant of using it, thus minimizing the hazard of uncertainty. There is, in general, only one bottle unstoppered a t one time making the replacement of the stopper automatic. 7. Bottles are available in a variety of sizes so that the refdl problem can be made practically nonexistent. The quantities used are so small that the total consumption of chemicals is less than may be anticipated. 8. Semimicro reagent bottles are generally so small that a student is not apt to use his reagent as ammunition for the water pistol. The teacher in charge of the class is conscious of refills and will immediately spot any extraordinary need for additional material. 9. It is true that some of the semimicro equipment is rather fragile. However, there seems to be no necessity for using the most fragile items, such as gas absorption bulbs. It has been our experience that students learn to handle the small equipment and to attain better technique rapidly, so that the total breakage is frequently less than with macro equipment. 10. Changes are always fraught with some difficulty hut the change from macro to semimicro procedures may well be fun. The additional interest which accrues from a change frequently more than compensates for the difficulty of instituting such a change. It is also believed that any difficulty in instituting this change will be more than compensated by the decreased effort in operating and maintaining the laboratory over . . a period of years. .. 11. There a$e many compelling reasons for serious consideration of the use of the semimicro technique in high-school courses. We may note first the matter of cost. This has been discussed in a number of publications.". lo, Our cost analysis is not presented in detail because its conclusion confirms in general that of the cited authors, that there is no substantial difference in equipping a laboratory with macro and semimicro apparatus. In converting an existing macro laboratory into a semimicro laboratory the total cost for a section of about 10 students, or any number of such sections run one after the other, is of the order of $100 to $150. This cost need not all he made in a single year and in any event is believed to be not prohibitive. The saving of chemicals seems very significant, amounting to a t least two-thirds of the cost with macro techniques. Hence the capital investment is rapidly amortized and future savings are assured. The saving in incidental costs such as plumbing maintenance, ventilation re-
' BECHTEL, W., AND J. A. FISHER, School S
Cand ~ Malh., 42,
647 (1941)
'@ARTHUR, P., J. A. BWROWS,0. M. SMITH,AND E. L. ADAMS, J. CHEM.EDUC.,18,385 (1941). Bun~ows,J. A,, 0. M. SMITH,AND H. THELAN, ibid., 26, 193 (1949).
OCTOBER, 1949
quirements, laboratory furniture maintenance, are in themselves very real. In addition we note that the small quantities involved in the semimicro technique minimize hazards such as explosions from partially filled bottles of hydrogen gas, or escape of large quantities of such toxic materials as hydrogen sulfide or chlorine. It is obvious that a student cannot break a half-liter bottle of concentrated sulfuric acid if his supply is restricted to 15 ml., with the small bottle normally left in its place in the reagent kit. It is felt that the cost and safety factors are so significantly in favor of the semimicro technique that school authorities m d the citizens from whom they derive authority will be impressed withhhe advantages mentioned. 12. The existence of more than one high school in a city may be an advantage in a transition from macro to semimicro procedures in that one school may be converted to the semimicro technique while the other school uses up the existing stock of macro equipment.
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This discussion will not answer all possible questions raised by all teachers. We have, however, endeavored to discuss all points which have been raised during the course of this investigation, and within those limits this presentation is substantially complete. We wish to thank the following teachers whose sincere cooperation has made this study possible: Dr. Dresser, Proctor High School, Utica, New York; Mr. Dudleston, Utica Free Academy, Utica, New York; Mr. Fillips, Whitesboro Central School, Whitesboro, New York; Mr. Giltner, Norwick High School, Norwick, New York; Mr. Hewitt, Madison Central School, Madison, New York; Mr. Knutty, Whitesboro Central School, Whitesboro, New York; Mr. McCabe, Whitesboro Central School, Whitesboro, New York; Mrs. Smith, Hamilton Central School, Hamilton, New York; Dr. Webb, Supervisor of Science, Syracuse, New York; Mr. Whitmore, Rome Free Academy, Rome, New York.
