QUANTITATIVE ANALYSIS FOR MEDICAL STUDENTS* LANDON A. SARVER, UNIVERSITY OF MINNESOTA, MINNBAPOLIS. MINNESOTA
It is frequently argued that standardized courses teach fundamentals as well as specialized ones, but there is little question that the instructor who succeeds in arousing the interest of his students, and in showing them how they may some day be able to use the information he imparts, secures better and more permanent results. Whenever they feel that they have been saddled with a course entirely foreign to their interests, and which can never be of any practical use to them, work becomes half-hearted, and they become more interested in merely passing the course than in permanently acquiring knowledge or skill. For a number of years I have been giving a course in quantitative analysis for pre-medical students and have frequently been put on the defensive because the men did not expect to analyze many iron or manganese ores after they became practicing physicians! With this in mind, I set out to evolve a new course which should illustrate fundamental principles just as effectively as the old conventional one, with material which would interest the student enough to secure his complete cooperation. The students themselves, upon being consulted, expressed unanimous preference for the new regime. The old course included three gravimetric methods, chlorides, sulfates, and iron; the calibration of a buret; and eight volumetric methods, Mohr's method for chlorides, soda ash, an organic acid, protein in flour, dichromate method for iron in ore, manganese dioxide in pyrolusite, manganese in iron ore, and free chlorine in bleaching powder. The latter method was unsatisfactory because of instability of the samples. In fact, none of the samples were very satisfactory on account of the labor involved in grinding, mixing, and analyzing them. The trend in clinical medicine is to avoid gravimetric methods and the use of the analytical balance as much as possible; hence it was decided to give only one gravimetric method, the determination of inorganic sulfates by precipitation as BaS04, which is still employed in physiological work. One duplicate is filtered through paper and ignited in an ordinary crucible, while the other is filtered through a Gooch, and dried in an oven. The calibration of a pipet has been substituted for the calibration of a buret, because many spent an unreasonably long time a t the latter. The mark is changed if necessary, and the flask then calibrated by delivering ten pipeffuls into it. The growing importance of colorimetric and micro methods in medical work is recognized by the introduction of Nessler's colorimetric method for ammonia. A simple, reliable procedure for this has been worked out and will be presented later. * Presented before the Division of Chemical Education of the A. C. S . at Minneapolis, Minnesota, September 12, 1929. 365
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As an example of a volumetric precipitation method, they may run either Mohr's or Volhard's method for chlorides, standardizing the silver solution against NaC1. For neutralization methods, an HCl solution is standardized against NalCOa; and a NaOH (carbonate-free) solution is prepared by diluting a concentrated NaOH solution (in which NazC03 is insoluble), and standardized against the HCl. They are then used to determine an organic acid, protein in flour, and inorganic phosphates. For oxidation-reduction methods, a permanganate solution is standardized against sodium oxalate, and used to determine calcium. Sodium thiosulfate is standardized against potassium dichromate in acidified potassium iodide solution; iodine solution is standardized against the thiosulfate or against arsenious oxide; and the two are used to determine formaldehyde in formalin. Finally, a bromate-bromide solution is prepared and standardized by weighing a definite amount and making up to the mark in the volumetric flask. Then i t and the thiosulfate are used to determine the phenol in a phenol solution. All except the flour, organic acid, and chloride samples are delivered in liquid form; and the students analyze aliquot portions. If desired, the stock sample solutions can be prepared in such a way that the mass delivered can be calculated by multiplying the volume by some simple integer. The students still get enough use of the balance in standardizing solutions, but all congestion is relieved. With the liquid samples, administrative work is greatly, simplified, and grading is more certain. In this new course, no work is given, which is not applicable to medical clinical work, yet fundamental principles have not been slighted.
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