a particular V B ~ C ~bond C ~ a t all t i e s , but for that bond under definite physical conditions. Furthermore, even a t a given temperature, the proportions of reaction products sometimes vary with the reagent used. Hence the position of the aoss-hair is affected not only by the physical but also by the chemical environment of the molecule. In view of such complexities, progress toward the development of a self-consistent system has naturally been slow. But beyond these inherent difficulties, many organic chemists have been further hampered by a strange predilection. For some reason they have chosen to identidy their cross-hair with the electron or the pair of electrons of the physicist. The misery which this infatuation has caused them is hard to estimate. They have become involved in problems of electrodynamics, spectroscopy, wave mechanics, etc. Since many of them have never had any training in such subjects, the outcome illustrates the unfortunate results which follow the attempt to "madly squeeze a right-hand foot into a left-hand shoe." No generally accepted system has yet resulted from these theories of valence which are usually called electronic, but which I prefer to call cross-hair theories. However, the reasons for attempting to advance in this direction are (as I hope to have shown) well founded and the results fairly deserve to be called promising. If organic chemists can ever be induced to develop the notations suitable to their own needs without regard to the quite distinct needs of other disciplines, much may be expected. Moreover, once they have taken this step, they may look hopefully for aid from their fellow scientists. As long as they remained wedded to their classic symbols, it was improbable that any outsider less experienced than themselves in manipulating these ideographs could be of much help to them. Having abandoned this practice, and having adopted a form of statement calculated to reveal, rather than to blur, the outlines of their problems, they may well find that considerable light on these 'matters is to be obtained from persons who are not prosptrtive contributors to future editions of Beilstein. A little friendly cooperation between scientific equals is likely to be more effective than much intellectual servility.
METHODS of WEIGHING by SWINGS. H. L. LOCHTE University of Texas, Austin, Texas
RECOGNIZED methods of accurate weighing with the analytical balance may be grouped into five-swing, equal-swing, and single-swing methods. The last two of these are often used but are not entirely satisfactory in the hands of the undergraduate student using the typical high-grade balance. The five-swing method is usually recommended in textbooks, but experience with data obtained with a number of sets of 5 swings indicates that the rest point calculated from a single set of 5 swings may differ from the average of 3 such sets by as much as 0.1 mg. Since the use of 3 sets of 5 swings makes weighing excessively tedious and time-consuming, especially when several students have to use the same balance, a study of various swing methods was undertaken in an effort to avoid the use of such an expensive method. Eight balances were selected a t random from a group of 42 balances bought since 1926 and in use by sophomore and junior students in courses in analysis. Three sets of 5 swings were obtained for each balance first with no load and then with 1 mg. overload. The 48 sets of data were then used in a study of the relative accuracy of 5-swing, 3-swing, and Pregl deflection data. In this. way 96 sets of 3-swing and Pregl data were obtained from the 48 sets of 5-swing data. The study shows that: (1) a single set of 5 swings often introduces an error of about 0.1 mg. due to poor reproducibility of rest point; (2) the average of 3 ,sets of 3 swings gives almost as reliable results as the average of 3 sets of 5 swings; (3) the average of 2 or 3 sets of Pregl deflection data agrees well within 0.1 mg. with the average of 3 sets of 5 swings and is much more rapidly and simply obtained. Experience in the use of the, Pmgl scheme with classes of 30 and of 230 students has been completely satisfactory, provided the balance is given a few minutes to, permit temperature equalization, the first swing is not used, and the balance is completely arrested betweem sets of swings.
DIVISION OF CHEMICAL EDUCATION-SAN
FRANCISCO
. 11 :2& 8. The Award of the High-school Chemistry Prize by. Wednesday Morning and Aflnnwn: the Chemistry Section of the A. A. A. S. (Pacific Division).. 9:O& 1. H. W. STONE. What Percentage of College Stndents Think? Do Your Students Think? 12:3&Divisional Luncheon. 2:0& 9. 0. M. SMITH, L. F. S H E EA ~N L A. ~ BURROWS~. 9:2& 2. E. F. DEGERING.Review Outlines as an Aid in the Teaching of Chemistry. Some Measurements of Laboratory Achievement in First3. P. A. LEIGHTON AND F. G . ANIBAI.. A Plan to Year College Chemistry. 9:+ Eliminate the Overlapping in High-school and College 2:20--10. T. G . THOMPSONThe Catalyst, a SeaGoig Chemistry Courses. Laboratory. AND D. J. H E N ~ S S Y A . Method 2:40--11. L. J. Woon n m C. W. FLm~wooa.. The Use of 10:00-- 4. J. B. MUENZBN for the Administration of Individual Assignments in ChemiSodium Paraperiodate far the Detection of Manganese h the Beginning Qualitative Course. cal Problems. 10:2& 5. ROBERT DuBors. The Ferric Thiocyanate Equi3:*12. N. D. C~i~nohns.Science InstFuction in the New libria. Chicago City Junior Colhpps 10:6. FLORENCE E. WALL. Training in Chemistry for 3:40--13. E. F. DEGEEING.The Intuitive Sense. the Cosmetic Industrv. 4:0@-14. L. A. TEST. A Periodic Table for LaboratomDisplay Constmctedof tbcElemnt%andTheir Cbmprmnd;. AND J. W. INCB. Twelve Years 1 7 R. K. C-&ON Business Meeting. of a Chemistry Contest.
