• A prelab assignment—things to be done before the laboratory period. This is the heart of the program, Dr. Thompson says. Students are directed to collect data and to outline experimental procedures they will need. • Laboratory assignment describing briefly the actual lab work. This is short and relies heavily on the prelab preparation. • A postlab paragraph summarizing the points covered, and perhaps pointing out to a student the things he should clear up. • A questions list. This contains calculations (with answers) paralleling, but not duplicating, the prelab problems. The lab record should resemble, as nearly as possible, that of a research scientist. All data are entered directly in the notebook. The notebooks need not be graded if lab exams are given on material which can be answered directly from a well-kept notebook. Staff. An adequate laboratory staff is essential to the success of this program, Dr. Thompson says. The prelab preparation means that early in the lab period a variety of questions will arise and these must be met by experienced staff. This may mean that such a program is not adaptable to large universities. But Dr. Thompson believes that even large numbers of students may be handled by starting the lab sections at half-hour intervals so that a senior instructor can get the lab session going before turning it over to assistants. In this way a teacher can work with 10 students during their first 30 minutes, while an assistant supervises 10 to 20 students who are already under way. Such scheduling also reduces peak loads on the stockroom, balances, and other facilities. The only equipment problem may be in providing enough analytical balances. Gustavus Adolphus faculty finds that two students to a balance is satisfactory when analytical balances with fractional weights are used. Dr. Thompson recommends one chain balance for each three students. If single-pan balances are used, fewer would be necessary, he adds. Besides being favorably accepted by students, Dr. Thompson says that a course of this sort makes possible more rapid progress in analytical chemistry and creates good laboratory habits from the beginning. The costs in staff and equipment are considerable, but not prohibitive.
Flame Spectroscopy's Stability Increased New instruments and better understanding of properties of flames increase usefulness of technique 145TH
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Instruments are available that greatly increase the sensitivity and stability of flame spectroscopy, according to Dr. W. D. Cooke of Cornell University, Ithaca, N.Y. For example, Dr. Cooke and coworkers at Cornell have developed an instrument that can reproduce absolute intensity values with a high degree of long-term stability. An average difference between first and last readings (taken at the beginning and end of eight-hour days for about 15 months) of recorded line intensities is only 1.3% for measurements (absolute values obtained without any recalibration) made on a solution containing 20 p.p.m. calcium in 0.1M ethylenediamine tetraacetic acid, Dr. Cooke says. A total consumption hydrogen-oxygen burner was used and the intensity of the 4227 A. atomic line monitored. Dr. Cooke points out, however, that close control of experimental conditions is essential to get such longterm stability. The degree of control found necessary by the Cornell workers for the several variables is: gas pressures, 0.25%; gas flows, 1.0%; amplifier gain, 0 . 1 % ; photomultiplier (RCA IP28) supply voltage, 0.01%; and solution feed, 0.5%. It isn't possible to control both the gas pressures and flows independently, Dr. Cooke says. Therefore, the pressures were controlled and the gas flows monitored to indicate sources of trouble, such as burner encrustation. The rate of solution feed is effectively controlled by a motordriven hypodermic syringe. It is rather remarkable, Dr. Cooke notes, that the response of a photomultiplier seems to exhibit no appreciable change in sensitivity over such a long period. He feels that the constancy of the burner geometry is the present limitation to a further increase in stability. It is also possible to increase the sensitivity of flame spectroscopy by proper
choice of a monochrometer. An instrument, such as a Jarrell-Ash Model 82-000 with a 30,000 line-per-inch grating is suited for flame spectroscopy, and improves the ratio of line intensity to source background noise, Dr. Cooke says. Chopper modulation of the light emitted from the flame source will also improve the signal-tonoise ratio. The signal is then amplified by a phase-sensitive detector tuned to the chopper frequency. More important than the new instruments, Dr. Cooke believes, are the research advances made in the complicated chemical and physical processes which occur in the flame sources. There is a distinct trend away from the previous empirical approach to flame spectroscopy. He points out that much basic information is obtained from line reversal temperature measurements, electronic population data, and ground state concentrations. One factor which has been troublesome to evaluate is the efficiency of conversion of salts in solution to their atomic state, and the subsequent formation of stable oxides in the flame, Dr. Cooke notes. But by using atomic absorption techniques (with line width data and transition probabilities), it's possible to obtain this information, then predict relative intensities of emission lines of elements, he continues. Flame Processes. Basic research has led to understanding of another process in flame spectroscopy, Dr. Cooke adds. The increased intensity of emission observed when organic solvents are used is caused by increased flame temperatures and more rapid evaporation of solvents. This gives a more efficient transfer to the atomic state of the element, he adds. It is even possible to predict the quantitative role that each of these factors plays in the over-all enhancement. In some cases, chemical excitation processes are also involved, and the intensity of the emission lines are greatly enhanced. Small contributions of chemical excitation (as contrasted to thermal excitation) were found in oxygen-hydrogen or oxygen-acetylene flames, Dr. Cooke says. But in airSEPT.
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hydrogen flames (especially with lines in the ultraviolet region), considerable nonthermal excitation was observed. He points out that the intensities of the Mg 2852 A. and the Tl 2768 A. lines can be predicted (within experimental precision) by the Boltzmann equation using oxygen-hydrogen or oxygen-acetylene flames. In the airhydrogen flame, however, the thallium line is 300 times more intense, and the magnesium line 40 times more intense than predicted. This indicates that chemical excitation is much more important than the thermal process, Dr. Cooke believes. In cases where population temperatures can be measured, the contribution of chemical excitation can be predicted and agrees with observed values. Dr. Cooke believes that by understanding the basic chemical and physical flame phenomena, it will be possible to design equipment which will eventually minimize many of the problems associated with flame spectroscopy.
Ability Grouping Is Successful In General Chemistry Two-year program is an attempt at a lecture-lab course that will satisfy students' needs 145TH
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Chemical Education
Students in the general chemistry course at Albion College, Albion, Mich., favor the chemistry department's experiment in ability grouping. Having gone through the first semester of the program's second year, 98% of the students say they like the system because it allows them to work at a level where they can get the most out of the course. Dr. Paul H. Carnell, chairman of Albion's chemistry department, says that students currently enrolling in freshman college chemistry courses represent a heterogeneous cross section of experience and background in chemistry, physics, and mathematics. Although the new high school programs in math and the sciences are available to more students each year, there are still many college freshmen who have not had the benefit of such programs as the Chemical Bond Approach (CBA) o r C H E M S . 58
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As a result, Dr. Carnell adds, it has become difficult, if not impossible, for instructors of freshmen college chemistry to offer a lecture-laboratory course at a level that will satisfy the needs of all their students. In an attempt to solve the problem, Albion tried a two-year experiment in ability grouping of freshmen in general chemistry. The class schedule has two objectives: • To use the hours usually assigned to general chemistry. • To keep the program flexible so that students could transfer from one ability group to the other while keeping the same lecture instructor. At Albion, general chemistry carries four semester credit hours with three hours' lecture, one hour lecture-lab, and three hours of lab each week. Enrollment averages about 125 students divided into four sections. All students are required to take a math proficiency test prior to registration in the general chemistry course. Students who pass this test are assigned at random to one of the four sections with no particular attempt made to use college board scores or other criteria. A one-hour examination covering the lecture material is given after three weeks. Students who receive A or B on this test are grouped in one section, and those who receive C or lower are placed in another section. The population of the ability groups is fixed until the next examination (exams are generally given every three weeks), when students are regrouped according to grades. Both sections use the same textbook and are exposed to the same core of topics in lectures. However, the higher-ability group receives a more mature treatment of the fundamental principles of chemistry in class sessions of a seminar type. In the other section, more time is devoted to difficult concepts, Dr. Carnell says, and the extra tutorial hour is used to help students with weak backgrounds in science and math. Laboratory. In the laboratory, the lower-ability group follows a more traditional schedule of experiments, while the other students are given more freedom in laboratory activities. The students like working at their own pace, according to Dr. Carnell. By working with students of similar ability, they are able to get a better understanding of chemistry. Both groups feel an added incentive to
work and are challenged by competition when they're among students of similar abilities. The C students appreciate the extra help and time spent on fundamentals, while the A/B group enjoys the chance to go more deeply into a topic. Students in both groups are less bored or discouraged, and are able to demonstrate their own abilities more readily. Dr. Carnell adds that the better students are stimulated to recognize the future possibilities in chemistry. Disadvantages of ability grouping are minor, Dr. Carnell believes. A few students feel a lack of continuity when they change groups. Also, some students in the lower group say that they are not challenged as much as if they were with the brighter students. Dr. Carnell says that the department will continue the experiment in ability grouping at Albion.
BRIEFS A three-year grant, to be used to train personnel in biometeorology, has been awarded to 11 midwestern universities by the Division of Air Pollution of the U.S. Public Health Service. The grant totals $238,016. Biometeorology is a relatively new science concerned with the effects of contaminated air on man, animals, and plants; it includes such fields as meteorology, physiology, geography, and zoology. Purpose of the program is to increase the number of professional workers engaged in activities for the prevention and abatement of air contamination.
An advanced research conference on gas chromatography will be held Feb. 3 and 4 at the University of California, Los Angeles. The program will include several distinguished chemists who will discuss their latest research in gas chromatography. The sixth short course in fundamental principles of gas chromatography will be held during the same week from Feb. 5 to 7 at UCLA. Its aim will primarily be to instruct personnel from industry. The approach will be nonmathematical and will stress theory only to the extent necessary in understanding the practical aspects of gas chromatography. The two programs are independent. Attendance at both programs will be limited with selection on a first come, first served basis.
