A NEW CODE SYSTEM FOR DISPENSING QUALITATIVE ANALYSIS UNKNOWNS* The composition of the unknown i s recorded in code on a ticket which i s issued with the unknown and later returned with the student's report. A code .finder, similar in mechanical construction to a slide rule, marked with ssymbols of elements and radicals a the central slide and casecutive numbers a the side scales i s carried by the instructor. The first number in the code on the ticket indicates the position of the key element, known only to the instructor, and thus fixes the position of the slide. The following numbers then indicate the composition of the unknown. Advantages of the system are: (1) cmnplete elimination of records; (2) the student report i s $led with the grade; (3) unknowns can be duplicated without duplication of code number; (4) reports are easily kept and tabulated; (5) adaptability to all ty$es of unknowns, (6) the system cannot be discovered or operated by students. Teachers of qualitative analysis ordinarily find that much of their time and energy is expended in dispensing, recording, and grading unknowns rather than in the actual teaching of the fundamentals Group -..I-. ...Grade .-. of the course. This is particularly true in large classes where the cooperation of several instructors or of the instructors and the supply-room keeper becomes involved. The result quite frequently is that the entire problem of the The ticket as issued to student with the dispensing of unknowns and un!mown. receiving the student reports on them is turned over to the Group ....I....Grade _.-!!? supply-room keeper, in which case the instructor has no knowledge of the contents of the unknown and is therefore handicapped in aiding the student in the laboratory or Smith, Signed .... .-. .-J.- -S. - -.- - - - - is forced to carry a trouhleI some pocket record. The same ticket as returned hy the student To eliminate the necessity with analvsis reuort. of teaching under these dis-
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* Presented in part before the Dividan of Chemical Education of the A. C. S. at the Atlanta meeting, April 7-11. 1930. 1811
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JOURNAL OF CHEMICAL EDUCATION
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advantages we have worked out the system which has been in use in our laboratories for several years, in which no records are kept by the instructor or in the supply room but only on a convenient ticket which is given to the student with the unknown. (Figure 1.) The system involves the use of a slide-rule type of "code finder," by the use of which the composition of the unknown is expressed numerically in a code which is recorded on the ticket given to the student with his unknown. This ticket, which is issued with the unknown, is subsequently used by the student as a form upon which to report his analytical results. The code finder we use in our supply room (see Figure 2) consists of two stationary scales of 50 equal space-divisions and a central slidink! scale likewise I'rcunri 2.--THECODEI i 1 ~ D E K divided. The left-hand stationary scale i s numbered downward from 1 to 25 and repeat, and the right-hand scale from 26 to 50 and repeat. The central sliding scale is divided into two columns. In the left-hand column in alphabetical order are placed the chemical symbols of the metallic elements and in the right-hand column are placed the chemical symbols of the acid radicals included in unknowns. The code finder used in the supply room is about 24 inches in length and the slide is counterbalanced by a weight enabling it to remain in any position and to be easily adjusted. It is mounted a t the right-hand side of the isSue window. For the use of the instructor in the laboratory a pocket model about 8 inches in length is convenient. The operation of the system requires the arbitrary selection of some key element by means of which the slide can be placed for decoding. This key element will be used ordinarily throughout the course but can be changed conveniently at any time if so':desired. The operation, which is quite simple, is best explained by an example. Suppose we have selected potassium as our key element and wish to read off the code number for an unknown containing Ag and Pb. When K, our key element, is placed opposite the numeral, 6, we see that 18 and 13 are opposite Ag and Pb, respectively, hence, placingour key number first, the code number of the unknown
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QUALITATIVE ANALYSIS UNKNOWNS
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is 6-18-13 or 6-13-18. This number is then written on the ticket and placed in the top of the test tube containing the unknown. Had we placed our key element K opposite 10, the code number for the same unknown would have been 10-22-17 or 10-1722. In the same manner other code numbers designating the same composition are 14-21-1, 16-3-23, 1-8-13, 13-20-25, etc. With two elements in the unknown there are 50 possible code designations and with three elements, 150 different designations are possible, yet each code number can represent only one definitecomposition. FIGURE 3.-~NKSOWNS WITH TICKETS READYTO The code number, deterBE DISPENSED mined in the manner deinches by 21/2inches scribed above is written on a small ticket, about (Figure 1) which can be easily rolled and placed in the top of the test tube containing the sample given to the student. No duplicate is kept in the supply room. The ticket is preserved by the student and is used as a form for his analysis report when it is returned with his signature to the supply room. The supply-room keeper checks his report against the code using the code finder, marks on the ticket the correctness of the analysis, and drops the ticket into a "ballot box" where it remains until it is desired to tabulate the results. In practice it will be found convenient, where there are large classes, to make up a quantity of the unknown sufficient for several samples and then divide i t into portions of suitable size for dispensing. The slide is then set and the code is read off for one ticket. Additional tickets for the remaining samples of the same composition can then easily be made by adding the same amount to each number in the code. Thus, suppose the first ticket were numbered 10-22-17, the next could be numbered (by adding 1) 11-23-18. Others would be: (add 3) 13-25-20; (add 5 ) 15-27-22, etc. Another series of different composition is then made up and coded in the same way. All unknowns belonging to one group of metals are placed in a container together and are dispensed to the student by the supply-
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JOURNAL OF CHEMICAL EDUCATION
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OCTOBER, 1932
room keeper without reference to the composition of the unknown. Thus, many unknowns can be made up in advance and quickly dispensed to the students in a rush hour. A group of unknowns with tickets ready to dispense is shown in Figure 3. One of the most attractive features of the system is the amount of work saved the instructor by having the student report his results directly to the supply-room keeper. At any convenient time the instructor can collect the results in tabular form to determine the standing of the class. About 3 hours' work has been found sufficient to tabulate the reports made by a class of 100 students where each student reported 20 unknowns. After using the system on several large classes we have found that it possesses these advantages over other systems: 1. There is no record book to be lost or perused by students if it is mislaid. 2. The student reports his analysis on the ticket issued with the unknown and his grade is marked on this ticket which is filed in the supply room. 3. Each unknown is dispensed with a code number which indicates its composition. 4. The unknowns are dispensed impartially without reference to the students' abilities. 5. Unknowns of the same composition can have very different code numbers but a given code number Fan represent only one composition. 6 . An instructor by the use of the pocket-model code finder can easily determine the composition of a student% unknown while he is assisting the student in the laboratory, even though he did not issue the unknown (it being understood that he confidentially knows the key element). 7. A student cannot decipher the code either from analyses he has made or by comparison of tickets with other students, nor could he operate the code 6nder without a knowledge of the key element. 8. There is no possibility of information being inherited from one class to another, for, should the system become +own, both the key element and the position of the key number can be changed. 9. The system is flexible and can be used for either acids, metals, or both acids and metals together in wet or dry unknowns.
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Note: Those interested in securing further information in regard to the codefLnders used in this system may communicate directly with the author or with Central Scienti& Co., Chicago, Ill.
