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SIMPLIFIED CORRECTION OF QUALITATIVE ANALYSIS UNKNOWN IRVING AMRON* AND KAROL J. MYSELSf
New York University, University Heights, New York
DETERKINING, with secrecy, the correctness of quali- of a few dashes is substituted for the customarylist of tative analysis results may be tedious and tiring where symbols. the number of students, of unknowns, of possible and The cards are printed on 4 X 6-in. cardboard, with actual ions are all large. instructions printed on the back, The master sheets The followingsystem, consisting of a student card and were drawn on red cross-section paper to match the 8 an instructor's master sheet.evolved.in our department, boxes per inch on the student card and copies reproproved its labor saving value and adaptability to in- duced by hlack~lineprinting for the several instructors. dividual teaching and grading habits of several instruc- When new unknowns are introduced, the master sheet tors. is easily changed. When quantitative estimation is The top line of the student card bears boxes corres- desired, the dashes may be replaced by numbers or ponding to all the possible ions, those' found being letters indicating the amounts of the various ions presindicated by an X. Space for preliminary observations, ent relative to some standard quantity. Each master student remarks, course identification and grading is sheet has room for 120 unknowns. provided. A detailed repoh of the analytical procedure Present. address: The Foundation, P,O, Box 504, in the student's notebook may be checked by the assist- princeton, N, J, ants ks they collect and initial the cards. . t Present address: Department of Chemistry, University of The number of the unknown from the assignment Southern California, Los Angeles, ~alilornia. book is entered in the top left corner of the card. Comparison of the card with the master sheet by juxtaposition is then accomplished* easily and speedily as shown in Figure 1. Any error is immediately apparent and marked by a vertical line through the corresponding box. On the master sheet, which takes only one or two hours to prepare, the ions actually present in the unknowns are indicated by DEDUCTIONS dashes corresponding to the boxes on the student card. Secrecy of unknown num- 1 ber is easily maintained while discussing the result with the student, if the instructor holds the card by its upper left hand corner, covering the unknown number with his thumb. The cards are not returned to ; L ~ + c ~ = s s : the student but filed in nu- : merical order of unknowns. Thus a review file is soon accumulated from which errors in unknown make-up or special difficulties soon become apparent. It is only through use F ~ W X 1. student card ~ ~ compared i ~ with . ~ e e t sheet. e ~ ( ~ hstudent ~ ~ = . i . . dsolvtion N ~ that one can fully appreciate e 207. In His Andy& H e Mi"-d Aluminum. Oxalste, and Borate and Reported E ~ r o n s ~ ~ .pot-ly the reduction of effortwhen b=ium end Cadmium.) The Extreme Right of the Master Shoot May 8. Used for Additional informl.tion observation of the position shown '
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