GENERAL CHEMISTRY LABORATORY PRACTICE: QUANTITATIVE EXERCISES G . N.
QUAM,
LONGISLAND UNIVERSITY, BROOKLYN, NEW YORK
There is great divergence of opinion among teachers as t o what should constitute the course in general chemistry. From the treatment of the use of the balance and of quantitative exercises in some laboratory manuals, the young teacher, no doubt, wonders how seriously that portion of the course should be treated. One author starts the student with "weigh an evaporating dish. . .and record the weight. Place in the dish pieces of roll sulfur and weigh. . ., ete." How can the student know when his weights are acceptable? Obviously, the instructor does not take time to check carefully his students' weighing in such procedures. Some authors do not even suggest practice weighing before plunging the student into a quantitative exercise. One of the functions of the general chemistry course is to prepare the student for courses that follow. It seems essential, therefore, seriously t o develop technic peculiar to analytical chemistry. The writer has found in his own classes that one method of helping the student to gain confidence in his ability t o weigh with the analytical balance is to give him an unknown weight sample just as he is given samples for qualitative and quantitative analysis. To accomplish this, polished strips (1.5" X 3") of stainless steel, weighing 25 to 30 grams, were numbered and accurately weighed. Each student, following a demonstration by his instructor, is given a numbered strip with its weight indicated on the envelope. As soon as he is satisfied tliat he can weigh accurately he is given two unknown weight samples in return foMhe known. When his weighings are completed the unknown strips are returned with his formal report by number and weight. When the accuracy demanded is developed the student is considered prepared to undertake suitable quantitative exercises. The strips made of "Allegheny Metal" and "Carpenter Stainless No. 4" have been used in a number of classes and are proving very satisfactory. At the outset, the large number of strips, after being numbered, were accurately weighed by instructors, the weights recorded for future reference, and the strips stored in boxes of twenty-four each, ready to be checked from the stockroom by the instructors when needed. The student's conviction that he can weigh accurately before entering upon an experiment which to him appears involved seems very apparent and is ample reward for the extra time and effort devoted to laboratory instruction. Through the use of these practically permanent weight samples in practice weigh'mg, the writer has observed in himself a rather marked change of attitude toward quantitative exercises in general chemistry laboratory courses. The observation seems to him worthy of report. 1474
