The USE of SEMIMICRO-METHODS in UNDERGRADUATE INSTRUCTION* ED. F. DEGERING Purdue University, Lafayettea Indiana
T
HE work of Pregl on quantitative organic microanalysis, that of Chamot on chemical microscopy, and that of Emich on microchemical analysis, have stimulated a far-reaching interest in micro- and semimiao-methods that is being recognized in our educational institutions. About seven years ago, in keeping with these newer developments, a start was made a t Purdue University toward the use of semimicro-methods in undergraduate organic chemistry. Year by year the course has been revised, the amounts of chemical decreased, the procedures improved, and the technic simplified until something approximating a semimicro course is being offered. Last year the undergraduate course in qualitative analysis was placed on a semimicro basis, and the results were very gratifying. At the present, some con* Presented before Lhe joint meeting of the Divisions of History 01 Chemistry and Chemical Education at the Fourteenth Midwest Regional Meeting, of the A. C. S., Omaha, Nebraska, May 1, 1937.
sideration is being given to the introduction of the semimicro-methods in the freshmen chemistry courses. TABLE 1 Qu~rrrrnerN 0 ~ r ~ ~ r PRssmT .u I N MACRO-PUALITATIVB
ANALVSIS
1015000 (as COI-I
C1 Br I N P lOIl000 1011000 1011000 1015000 1013000 (as C1-) s I (as I-) (as NO8-) (aa POI?
(as So,-]
C 115000 (ar COa?
CI Br 1 /I000 lll000 (an CI-) (as Br-)
113000 (a5 SO.-)
C
I N P lIl000 115000 113000 (as)'1 (as NO%-)(aPO,-1
S
1013000
S
TABLE 3 Qvnlrrmres READILYD B T ~ C TI N~ D SBM~MICROQUAL~ATTTT ORCANIC ANALYSIS
C1 Br I N P S 1155,000 1/25,000 1126,000 1125,000 1125,000 11100,000 1127,600 (as C O r ) (as C1-) (ar Ri-) (as 1 - J (as C N - ) (as PO4-] (an S')
C
A beginning has been made; much remains to be done. In an evaluation of the use of the semimicro-methods
in undergraduate instruction, there are two distinct phases of the topic which deserve special consideration: the advantages to be derived from the purely instructional viewpoint, and the economies to he effected in so farasthe administrationof thelahoratoryisconcerned. In discussing the advantages to be derived from the purely instructional viewpoint, i t may be taken for granted that the fourfold objective of laboratory instruction aims a t the acquisition of technic, the development of the senses, the assimilation of factual knowledge by 6rst-hand experimentation through a logical interpretation and correlation of the results, and the preparation of intelligible reports. The student should be taught to do correctly, to sense accurately, to think clearly, and to report intelligibly. With the use of the usual macro-methods, there has been a tendency to neglect the proper acquisition of technic inasmuch.= the quantities of materials worked with do not require accurate and careful manipulation on the part of the student. The semimiao-methods, on the other hand, call for an added degree of technic that gives the student an invaluable training in accuracy and precision that will be of inestimable value to him in almost any vocation to which chance may assign him. This is amply illustrated by a consideration of Tables 1, 2 and 3. The data in these tables indicate that the quantities of materials for maao-methods are a t least ten times as great as those normally employed in the semimiaomethods. An ample spread exists, however, between the quantities normally used in the semimiao-methods and the minimum detectable amounts of the constituents. The present status of the procedures might justify such a spread, but as methods are improved the amounts of reagents used in the semimiao-methods will be decreased proportionately. It is difficult to evaluate the effect of smaller amounts of materials in terms of the acquisition of technic, but all must agree that working with a milliliter of solution instead of ten milliliters of solution, must, without question, enhance the acquisition of technic on the part of the individual student. The semimicro-methods, moreover, call for more careful observation on the part of the worker. The student must he alert if he is to detect slight changes that are to be taken as indications of a reaction between the reagents. He must be able to detect the formation of a slight precipitate, the liberation of a small amount of heat, the escape of traces of a gas, or the presence of a faint odor. He must he able to see, to feel, and to smell. He must sense accurately. The development of the power to think clearly and of the ability to record intelligently may not be enhanced by the use of the semimiao-methods, but the writer is of the opinion that the student who does more correctly and senses more accurately will think more clearly and record more intelligently. It would seem, then, that in so far as we are concerned with better instructional methods, the semimiaomethods have ample justification.
In considering the economies that may be effected by the adoption of the semimiao-methods, one must evaluate the ca~acitvof the laboratory, the reauirements for apparatus, and the consumpti& of chemficals. The capacity of a laboratory is a problem of increasing concern & the enrolment figures begin to mount. A very careful consideration of this phase of the problem has indicated that the space normally allotted to six freshman students per semester (six laboratory sections) can be made to accommodate twelve freshman students per semester (twelve laboratory sections). In other words, the storage space for the semimicro-apparatus is about one-half of that necessary for the macro-apparatus. The standard freshmen lockers a t Purdue, for example, measure 9 X 18 X 24 inches, but a locker 9 X 9 X 24 inches would accommodate the necessary apparatus if the semimicro-procedures were adopted. This means, of course, that a given laboratory can accommodate just twice as many students. Whiie twelve sections per week in a given laboratory might not appeal to the average instructor, i t will certainly make an appeal to the taxpayer. In the courses in qualitative analysis and organic chemistry, similar economies with respect to storage facilities could be effected by the introduction of the semimicro-methods. The savings on investment in apparatus will be determined somewhat by the particular course under consideration, hut in most cases this saving will prove to be significant. The economies in the consumption of chemicals, obviously enough, should be about ninety per cent. Actually, the figure is more correctly represented by fifty to seventy-five per cent., due to the fact that as one decreases the amount of materials used, the percentage waste is proportionately higher. In a junior organic course, actual calculations based on chemicals required by the semimicro- as compared to the macroprocedures indicate a saving of fifty per cent. In this same course, this represents a saving of about five dollars per year per student. It is estimated that a saving in chemicals of a t least one dollar per year per student could be effected by the use of the semimiaomethods in freshman chemistry as a substitute for the usual maao-procedures. In qualitative analysis a similar or even greater saving might be effected. In this day of increasing costs, more attention ought to be given to these possible economies. On a sevenfold count, then, the semimiao-methods appear to he superior to the usual maao-methods. (1) The student learns to do more correctly. (2) He is compelled to sense more accurately. (3) He is encouraged to think more clearly. (4) He is inclined to record more intelligibly. (5) The cost of his working space is only one-half as much. (6) The cost of his apparatus is reduced to about onehalf as much. (7) The cost of his chemicals is only ten to fiftyper cent. as much.
