ADVANTAGES OF THE SEMIMICRO TECHNIQUES FOR GENERAL CHEMISTRY' OTTO M. SMITH and 1. AUSTIN BURROWS Oklahoma A. and M. College, Stillwater, Oklahoma HERBERT THELAN University of Chicago, Chicago, Illinois
ATTHE Oklahoma A. and M. College we started experimenting on the semimicro laboratory procedure in 1930. The first laboratory manual to our knowledge is one entitled "Practical Chemistry by Micro-Methods,"% written by Dr. Egerton Charles Grey in 1924. Dr. Grey, a t that time, was professor of Chemistry a t the Government Medical School, Cairo, Egypt. In his preface, he writes: "It must be evident to many that the time has come for a change in some of the methods of teaching practical chemistry. Classes seem to get larger every year, and the standard is being gradually raised. It follows that many experiments which could once be performed by each individual must perforce be omitted, and there is a tendency to meet the situation by adapting the practical course rather to the convenience of the laboratory than to the individual needs of the students. There is nothing which a t present is done by students with large apparatus that cannot be done with the micro-method, but there is much that can be done with small apparatus that is sheer waste when done on the larger scale." We used this hook for one year but found the exercises unsuitable for us, but the plan and ideas were highly intriguing. So for the past 13 years experiments and changes have been taking place; changes have been made from semester to semester and year to year in the selection of experiments, alteration in directions, and inclusion of new ideas; in the assortment of equipment in the students' lockers; in the arrangements of reagents placed before the student or on the side shelves; in the design of the laboratory table, as to space per student, location of reagents, sinks and services as hoods, distribution of hydrogen sulfide, and in providing seating for students to reduce fatigue; and in the arrangement of facilities to provide for greater convenience in the use of notebook, laboratory manuals and texts and to protect them, as well as the students' clothing, from damage due to spilt acid, chemicals, and water. Over this period the present laboratory manual, "Semimicro Laboratory Exercises in General Chemistry," was developed by Messrs. J. Austin Burrows, Presented before the Division of Chemical Education a t tho 113th meeting of the American Chemical Society in Chicago, April, 1948. %GREY,E. C., "Practical Chemistry by Mior-Methods," W. Heffer & Sons, LM., Cambridge, England, 1924.
Paul Arthur, 0. M. Smith,3and associates. Originally, many of the laboratory exercises were written for the customary macro scale experimentation. They have all now been changed for the semimicro scale. Thus the data and conclusions stated in this report have been obtained by comparing the results and observations using the two laboratory procedures, macro and semimicro, when using relatively the same exercises by the same teachers. The writer wishes to remind his readers that the data, with few exceptions, are those obtained from only the laboratories of the authors a t Oklahoma A. and M. College. This paper is in two parts, the one deals with the relative advantage3 and disadvantages of the two procedures as they may influence the learning of the students, the acquisition of certain laboratory skills, their attitude toward chemistry, and the grades they received in the chemistry course; the other deals with the administration of general chemistry as regards to costs for equipment, breakage, and apparatus provided the student, the capacity of the laboratory, maintenance costs, health and accident hazards. One of us spent a year making a careful study of the two laboratory methods.' These experinients were carried out using nine classes taught by five different instructors. From this group for the fall semester two matched groups of 48 students using each method were compared. These 96 students, in several groups, were distributed in four classes of three instructors during the second semester. The precision of matching was considerably better than the precision with which the instruments used could show any difference. The two groups were compared using specially constructed measures for the following objectives: knowledge of chemical concept, ability to interpret data, ability to evaluate factors in experiments, ability to predict outcome of experiments, ability to explain finding in ex-
' BURROWS,J. A., P. h ~ n wAND , 0. M. SMITH,Yiemimicro Lahorrttorv Exercises in General Chemistrv." Macmillan Company, 1942. 4 "The Apprrtisd of Two Methods for Teaching Scientific Thinking in General Chemistry," by HERBERT%ELAN, unpuhlished Ph.D. Thesis, University of Chicago, 1944. Also extensively abstracted in the Journal of Experimental Eduealim, September, 1944, pp. 58-75, under the title, "A Methodological Study of the Learning of Chemical Concepts and of Certain Abilities to Think Critically in Freshman Chemistry."
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periments, skill in critical reading of statements of chemical functionality, and opinion about good laboratory techniques. Of the 34 comparisons possible on the above seven sections of the tests, 23 show slight but insignificant advantages for the semimicro group. This might he accounted for by known differences between the students or more likely by known differences in the enthusiasm of the instructor for the two methods. The macro certainly is not superior to the semimicro method, but the superiority of the semimicro is not demonstrated to be due solely to the difference in the size and the design of the apparatus. In any case the differmce is not educationally significant. The impressions of some of the instructors were that the semimicro procedure permitted the student to perform more experiments in a given time than when using the macro procedures. As regards the administration of the freshman laboratory, these are the conclusions reached by the staff at Oklahoma A. and M. College after using micro procedures and observing classes for about 12 years. COSTS
Equipment in the Desks. On comparing the apparatus check lists, there is less difference than one might expect. In the semimicro method, although smaller-size pieces are used, a greater variety is included, 39 items for the macro equipment and 56 for the Semimicro. Value of all equipment in the dekk, including nonreturnable~and excluding ring stands, tripods, reagent bottles and chemicals, based on costs for 1947, is for the macro set $6.74 and for the semimicro set $8.39. Consumables. For semimicro the breakage and consumable~other than chemicals per student for three hours of laboratory per week for one semester is estimated as: 31 cents for 1944, 34 cents for 1946,42 cents for 1947. Two other schools report cost of 30 cents and 75 cents~*~ Der student Der semester. Chemicals. The cost of chemicals uer student uer semester is estimated a t 75 cents to $ l . i 5 for the peiod of 1943 to 1947. A comparison of the amount and cost of chemicals used in the same experiments, involving 86 different items, was 5'/* times more expensive for the macro than for the semimicro. One complete set of all reagents is placed on the laboratory table for each four students. On the reagent racks the large size bottles are only 4 on. instead of the usual 16- to 32-02. size. Centrifuges. Centrifuges are used in place of filtering. In the macro procedures filter paper was used, hut in the semimicro occasionally or not a t all. At present one centrifuge per 24 students is sufficient. The price of the Waco centrifuges purchased this year was $37.50 each. During the past years we have not had any centrifuge failures. Of course they are periodically oiled and cleaned in our own shop and only one has had to he returned to t,he factory. A conse~ativelife estimate of a ~
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centrifuge, in our opinion, is ten years. Thus the cost per centrifuge per student for one semester is only 10 cents each, or 20 cents per year. Hydrogen Sulfide. Since such a small amount of HzS is needed, the extensive installations with separate rooms, hoods and exhaust systems, and dispensing arrangements for liquid HaS are not needed a t all. Ferrous sulfide about the size of a BB shot is used in a 75-mm. test tube with a drop or two of dilute HC1. These amounts in even the larger classes of 100 to 200 students do not release sufficient H2S to become a nuisance. Costs. The total cost per student for a 3-hour lahoratory per week for one semester, for all services provided the student--chemicals and apparatus, labor and maintenance and desk reagents-is estimated as: $3.12 for 1944, $4.15 for 1946, $4 for 1947. Several schools were asked to submit figures of costs, hut most indicated that the values so submitted are estimates; few if any keep records of costs per class. The estimates given from six schools are $2.50, $2.85, $3, $4.50, $7.50, and $8. One small college reports that the actual cost from records maintained is $7.21 per student per semester, plus the chemicals used. HEALTH HAZARD
In the traditional or customary laboratory, using macro techniques, the teaching staff has always dreaded the halogen exercises. You know well what I mean-sore throats, irritated eyes, colds, and frayed tempers. With the semimicro method, even though there is some odor and irritation, the extent is so small that not even hood ventilation is required. As regards the fire hazards in the use of ether, alcohol, sodium, and other inflammahles, such small amounts do not require the usual precautions. We have had fewer accidents and less serious ones using the semimicro quantities. There are fewer clothes damaged, due to smaller qnan.. . . . . tities of chemicals used. SPACE
We have experimented with various length of space allotted to the student and have reached the conclusions that the effective minimum is 42 inches; below this the average student is crowded. We have used lockers of various sizes from 10 in. wide by 48/4 in. high by 20 in. deep, which is too small, to the lockers originally built in the desk, about 17 in. wide by 35 in. high by 20 in. deep. This space accommodated a t that time one student's equipment; that space is now adequately accommodating 4 students. Thus a laboratory table 14 feet long by 4 feet wide which formerly housed the equipment for 14 students now takes care of 56 students, an increase of four times. The size of the lockers we are now using is about 9S/4in. wideby 83/rin. high by 16 in. deep.
With less corrosive fumes, absence of hoods, small amounts of chemicals used and spilled, the costs of maintaining the laboratory are considered less. Plumbing repairs and 0 t h work done have heen materially less. As a summary, Dr. Bede Ernsdorff of St. Martins College writes, "The advantages of semimicro procedures, in our estimation, go far beyond the show in
costs, since these are ultimately cared for by student fees anyway. In fact, the over-all costs of the semimicro are equal to, or even above, macro procedures during the first years of a changeover, because of investment in special containers, centrifuges, etc. The neater and more rapid techniaues, the easier accessibility of supplies to kach student, the reduction of obnoxious odors even without forced ventilation, smaller working and storage space, are all a few of the advantages that we would not like to be without."
