2912
JOURNAL OF CHEMICAL EDUCATION
DECEMBER, 1930
differences and rigidity of structure are at once apparent from the tetrahedra models. The strain theory is readily shown by the tetrahedra models. The model on the right in the photograph below may be taken torepresent malonic acid which does not yield a true anhydride. T o eliminate water would draw the free ends together which would put the molecule under too great a strain. The next acid, succinic acid, containing four carbon atoms forms an anhvdride: the strain produced in tying MODEL OF ACETYLENE S HOWING REPRESENTATION OR np the ends is much lessTRIPLY BOUND CARBON ATOMS, ALSO MALONIC ACID ened. Singly bonded carbon atoms are represented by joining the tetrahedra, solid angle to solid angle; doubly bonded carbon atoms are represented by the tetrahedra having an edge in common, while the triple bond is represented by a plane in common. Such is pictured in the last figure by acetylene. In the presentation of this topic the author has used line drawings freely. However, in presenting the subject to the class, the use of tetrahedra makes these line drawings unnecessary and the instructor is free to devote his entire attention to the demonstration with a consequent gain in time and clearness of presentation.
Literature Cited ( I ) For these relationships see PORTER, "The Carbon Compounds." revised edition, Ginn and Co., Boston, Mass., 1926, pp. 130-6.
Speed of Snper-Sound Waves Tells Squeezability of Chemicals. Measurements of the speed of ultra-sound waves, vibrating 400,000 times a second, twenty times as fast as the shrillest audible sound, in various solutions of chemicals were described a t the Atlanta Meeting of the A. C. S.by three Johns Hopkins University chemists. Speaking before the section on physical and inorganic chemistry, Drs. E. 8.Freyer, J. C. Hubbard, and D. H. Andrews told of their work with the sonic interferometer. From such measwemats can be determined the compressibility, or "squeezability" of the liquid. The chemicals tested were solutions of chlorides, bromides, and iodides of potassium and sodium, including common salt.-Science Senrice
