We do think that there are some things that can be improved, and some changes t o be tried. A~parent~ly many chemists agree. One of the most encouraging things about the Study so far is the willingness and enthusiasm among those who have been asked to participate on all levels, and the interest which the high schools and their teachers have already shown in the Study. Let me cite one statistic. Twenty-four teachers were invited to come to Claremont in August and become familiar with the materials. The teachers were to perform all the laboratory experiments and thoroughly discuss the text. They then were to decide whether or not they would use the materials in their classes. I t was made clear that their presence in Claremont involved no commitment to use the mat,erial, but that if they did use it, they were to adhere closely to it. All 24 decided to use the materials. Now, I cite this as an interesting statistic only because I want to hasten to add that many of them are skeptical as to how well the materials will succeed.
Shirley w. Gaddis Bethany College W e s t Virginia
The staff has its doubts too, but criticisms from all concerned are being actively gathered. Staff members are meeting once a week throughout the year with the teachers. In fact, four of the staff are actually teaching the course in two high schools. The Study is also investigating films (moving, filmstrip, and still), monographs, teacher's guides, lecture experiments, and models, with a view to producing such materials as will enhance the course. Suggestions are actively solicited for staff consideration. Our long term plans are to produce a tested course by the fall of 1963. It will, by then, he in its 4th or 5th revision. At that time we may have some better idea as to what can be done to make high school courses more effective than they are now. The over-all aim, then, is to generate and collect ideas which will not so much outline a course, but set a tone and suggest directions in which the first course can move so that it honestly presents a contemporary view of chemistry and its continual growth.
A Simple Filtration Technique for Gravimetric Determinations
Most chemistry teachers recognize the desirability of using more gravimetric experiments in the freshman laboratory. However, if a precipitate is to be separated and weighed, the planning for the experiment presents difficulties. The teacher must feel sure that his students have the skill to carry out the filtration techniques. He must also be sure that there is in his stock room the necessary equipment. This means that a rather expensive inventory of Gooch or sintered-glass crucibles has to be maintained. This paper offers a method by which the filtration can be done using a simple technique and inexpensive apparatus. The basic idea is this: Two 9-ern Whatman No. 1 filter papers are placed on the balance pans and carefully tared against each other by trimming one paper or the other with scissors. If especially good results are desired, the handling of the papers should be done with tweezers. The papers are folded together to make a single filter. The precipitate is filtered on the top paper of the pair. The precipitate and paper are washed thoroughly and allowed to dry together for one week. The papers are then separated and the top paper with the precipitat,e on it is weighed using the bottom paper as a tare. The assumption is that since the two papers are subjected to the same treatment throughout, the change in weight will be the same for both papers. Thus, the weight of the precipitate is the sum of the weights which must be added to the tare pan. To illustrate the possibilities of this technique, the determination of the per cent silver in a dime has been used. In a private communication, the General Coun-
sel for the Treasury Department states that, in his opinion, it is permissible to destroy completely U. 8. coinage. This is not the same as illegal defacing of currency. T h e dime is cut in half to make a sample which is weighed to +0.001 g. The sample is reacted with 4 ml of 8 M HNOi by warming gently. One ml of 18 M H-SOa is added to aid the rapid precipitation of the silver as AgCl by 3 ml of 6 M HC1. The precipitate is warmed and stirred for 30 min., and the supernate then poured through the 2-paper filter. The precipitate is washed by decantation in the beaker as well as later on the filter until a negative Cl- test is obtained. The papers and precipitate are dried one week. By using three acetone washes the AgCl can be weighed the next day. The papers are separated and the precipitate weighed as explained above.
To test this method a total of 74 determinations was made over a period of years. Summarizing the results obtained: The highest value obtained in the 74 analyses was 90.2% Ag; the lowest value obtained in the 74 analyses was 89.76% Ag; the mean per cent was 89.92%; (U. S. coin metal is 90% Ag). The 1i.M.D. of this series of 74 values was 1.4%. Those teachers who are skeptical of the precision and accuracy possible by using this technique should try it before judging it. I t seems pertinent in this context to say that this technique has been used in our sophomore course in quantitative analysis for the gravimetric determinations of the soluble chloride and sulfate. Starting with semimacro samples of 100 mg our students have been reporting results that cannot be distinguished in accuracy and precision from the results obtained by using the customary crucible procedures.
