V O L U M E 21, NO. 11, N O V E M B E R 1 9 4 9 for it contains many practical hints to supplement their theoretical knowledge. It also should prove a valuable reference for the experienced chemist who has only an occasional metal sample to analyze. The chemist who is in daily contact with metal analysis will find it interesting as a means for comparing methods in common use in England with those he is using.
H. F. BEEGHLY
A Simplified Course in Elementary Qualitative Analysis. Bruce
+
E . Hartsuch, editor. 192 ix pages. D . Van Nostrand Co., 250 Fourth Ave., Kew York, N. Y. Price, $3. This book has been written to review and extend the student’s knowledge of the principles of general chemistry, to present the subject matter in a brief simplified manner easily understood by the beginner, to assist him in the use of theoretical tools, to direct him in a careful explicit way, training him to do dependable work, to guide him in making proper and significant operations, and to impress him with the importance of sound theoretical foundations on which to build manual operations.
Analysis of Gases by Absorption and Combustion SIR: An error of omission in our recent paper entitled L‘Analysis of Gases by Absorption and Combustion” [ANAL.CHEM., 21, 1105-16 (1949)] has been brought to our attention by Robert D. Schultz of the Applied Physics Laboratory a t The Johns Hopkins University. The addition of potassium iodide was omitted in the directions for preparation of the potassium iodomercurate reagent which is used for the selective absorption of acetylenes. The correct procedure for preparing this reagent is as follows: Slowly stir 100 ml. of 50y0 potassium hydroxide solution into a solution containing 25 grams of mercuric iodide and 30 grams of potassium iodide in 100 ml. of distilled water. It is preferable to prepare the quantity needed each day from these two stock solutions. I t was also noted by Dr. Schultz that, in the preparation of cuprous chloride reagent as described in our paper, sodium chloride mav precipitate from solution. Should this occur, it is our practice to withdraw and use the supernatant solution. F. R. BROOKS Shell Development Co. Emeryville, Calif.
Frequency Errors in Timing with Electric Clocks SIR: The conclusions drawn by Craig, Satterthwaite, and Wallace in the article “Frequency Errors in Timing with Electric Clocks” [AKAL.CHEM.,20, 555 (1948)l are apparently too broad when they state that “. . . . the frequency errors revealed in this study are probably representative of those to be expected in using the line current available in any large American city.” Some unfortunate errors have crept in on observations of time made by the use of local power line frequencies.
1433 The subject matter is presented in the light of the modern theory of ionization as modified by Debye, the laws of mass action and chemical equilibrium, and the electronic changes taking place during chemical reactions. Prefaced by a section on suggestions to beginning teachers, the book is divided into four parts. The first or theoretical part of the book deals with a discussion of solutions, ionization and disassociation, homogeneous and heterogeneous chemical equilibrium, amphoteric compounds, atomic structures and types of bonds, redox reactions, and hydrolysis. The laboratory parts of the book include studies of 21 cations and 11 anions. The actual manual operations are clearly outlined and are interspersed with pertinent questions which can be answered in the laboratory. Part IV is devoted to a glossary of signs and symbols and tables of commonly used solubilities, ionization constants, solubility products, the periodic system, test solutions, etc. The course provides for the needs of the general student as well as for the student preparing to enter the profession of chemistry, though more laboratory work should be expected from the latter. It is advantageously presented from the instructor’s standpoint. W.A. KIRKLIN
There is no criticism of the report on the system controlled by Pittsburgh as reported. However, we have found errors of much greater magnitude for the Philadelphia system, of which Baltimore and Washington are a part. By use of a differential frequency recorder described in the August 1949 issue of the National Bureau of Standards Technical News Bulletin, it is possible to obtain a continuous, automatically plotted graph of drift in frequency of the commercial power line with respect to a crystal controlled standard frequency accurate to one part in 5 X IO7. By choosing suitable coordinates, the graph can be made t o indicate the drift of the “time error.” A detailed study of some of these graphs shows frequent errors in a IO-minute interval three times greater than the maximum error ever recorded as reported by Wallace and his associates. The cause of the discrepancy between Wallace’s observations and our own lies, I believe, in the difference between the total generating capacity of the two power nets concerned. When two or more alternating current generators are connected in a parallel line, and one of the generators fails to contribute its share of the load and tends to turn over a t an electrical frequency lower than that of the line, that generator becomes in effect a motor, loading the line rather than feeding it. This load is dissipated by causing the “slow” generator (acting as a motor) to continue rotating at an electric frequency very nearly equal to the line. Conversely, when one generator tends to rotate a t an electric frequency greater than that of the line, it attempts to supply enough power to the line to place all other generators on the line in the “motor” category and bring their speed up to its own. There are automatic cutouts to remove a generator from the line altogether if its phase drifts too far from that of the line. Thus, in a well monitored net all generators rotate at the same electric angular velocity. For the frequency of the net to increase or decrease, the inertia of all armatures must be overcome, and all armatures will accelerate or decelerate together; and the greater the total inertia of the armatures on the line, the more difficult it will be for the net to accelerate. Hence, it follows that other factors being equal, the larger the power net supplying the city, the greater will be the frequency stability.
A N A L Y T I C A L CHEMISTRY
1434
I n the article, the authors did not state that their intervals were adjoining; they merely stated that the intervals were “not overlapping.” If the intervals were not adjoining, it would be necessary to have a very precise method of sampling in order that they might have a true representation of conditions. By use of our apparatus we did not have to meet the problem of sampling, because our intervals wele all adjoining. H. -4.BOWMAS Time Section National Bureau of Standards Jvashington, D. C. SIR: Bowman’s observations concerning frequency errors in timing with electric clocks in the Washington area are significant in that they indicate the magnitude of such errors for another area and another power network. It is obvious that our conclusions were too broad when we stated that the frequency control in other metropolitan areas was probably comparable with that in the Pittsburgh area.
Although there seems to be no doubt that frequency errors in this locality are less than in the areas supplied by thePhiladelphia power network, in my opinion the cause of the difference is not definitely established. Bowman is of the opinion that the difference in the total generating capacity of the two systems is responsible for difference in quality of frequency control. Undoubtedly this is a factor. Perhaps it is the major factor. However, the character of the industrial load borne by the Pittsburgh system is of such a nature &s a t least partially to nullify the capacity factor. I have recently learned that the Pittsburgh system has an electronically operated automatic system for frequency control, whereas the system servicing Washington is, to the best of my knowledge, controlled manually. This may also contribute to the more precise control of frequency here. The time intervals chosen in our study were all adjoining. W.E. WALLACE University of Pittsburgh Pittsburgh, Pa.
Electron Microscope Society of America F. -4.IIAMM, General Aniline & Film Corporation, Easton, P a .
HE seventh annual meet,ing of the Electron Microscope SoTciety of America was held a t the National Bureau of Standards, Washington, D. C., on October 6, 7 , and 8, 1949. The attendance was the largest to date, with some 250 people attending. E. U. Condon, director, Sntionnl Bureau of Standards, and F. 0. Schmitt, president, Electron Microscope Society of America, opened the meet,ing with a few introductory remarks. L. A . Chambers, Camp Detrick, Frederick, &Id., who served as chairman of the committee on local arrangements, and R. G. Picard, Radio Corporation of America, Camden, K.J., who served as program chairman, deserve much credit, for planning this successful meeting. The customary Friday evening banquet was held a t the Wardman Park Hotel. For the first time in the history of the society, no after-dinner speeches were given. Incumbent president F. 0. Schmitt introduced president-elect R. W. G. Wyckoff, National Institutes of Health, Bethesda, Md., who will begin his term as president of the society in January 1950. The program of this meeting is abstracted below; only those CHEMISpapers of general interest to the readers of ASALYTICAL TRY are included. Consequently the papers dealing with biological problems are omitted. The first session consisted of contributed papers dealing primarily with instrumentation. Temperature of Electron Microscope Specimens. G. D. SCOTT FRANCES D a w ~ sUniversit,?. , of Toronto, Toronto, Ontario, Canada.
AKD
Although tremendous thermal energies may be generated (localories per second) in a strongly electron absorbing specimen, :t good portion of the heat is dissipated by radiation to the walls of the instrument. Stable materials such as alumina or sodium chloride can be made to melt. The Formvar substrate absorbs little infrared radiation, so that it absorbs heat only where contact with the specimen is made. Thus, the very high temperatures experienced by electron microscope specimens under strong illumination by elect’ron beam must be taken into consideration. Vibration Studies Related to Electron Microscopy. F. A. 1-I.kmr . ~ X D F. C. SXOWDEN, General Aniline & Film Corp., Easton, Pa. Ari oscillographic trace due to (L voltage generated piezoelectrically by a phonograph (crystal) pickup can be used to detect arid measure vibration, and as a guide for properly locating an electron microscope where building vibration is a problem. Furthermore, this scheme makes it possible to correlate qualitatively image shift’swith vibration amplitude. Because building vibrations are usually only periodically prohibitive, the scheme described can be used a8 a guide for high resolution electron microscopy. The circuit and calibration procedure were briefly described.
Performance Tests on the RCA Model EMC Electron hlicroscope. S. G. ELLIS,RCA Laboratories, Princeton, N. J. I t is not possiblz to increase the resolution of this instrument beyond about 50 A., primarily because the angular aperture of illumination cannot be further lowered. This value is not ordinarily realized, but by mechanically modifying the specimen stage (to prevent thermal drift) and by improving the objective lens asymmetry, a resolution of 50 A. is possible. The normal wide angle cone of rays from the projector causes reflection of extraneous electrons onto the photographic plate. Insertion of a projector aperture is therefore desirable because image contrast is improved. Testing of Electron hlicroscope Objectives. JAMES HILLIER HENRY FROVI,.~, RCA I,aboratories, Princeton, N. J.
ASD
Virtually all electron microscope objective pole pieces exhibit some astigmatism. By photographing a test object (carbon black) defocused by known amounts in the range 1OOp to - 1001 a series of Fresnel fringes is recorded. A chart illustrating the width (and number) of these fringes versus known object displacement, but having used a well corrected objective pole piece, is then prepared. The image at the same magnification, recorded with the uncorrected lens being tested, is compared with the chart. One direction through the image must be in sharp focus, the nature of the fringe along the perpendicular direction is then used to assign a value (in microns) to the lens asymmetry. An asymmetry of less than a few microns is n prerequisite to high resolution.
+
Technique for Comparison of Identical Surface areas in Light AND RUTHH. and Electron Microscopes. ERNESTF. FULLAM PETCHER, Knolls Laboratory, General Electric Co., Schenectady, N. Y. This technique facilitates the correlation of light and electron micrography of the same metal surface. An acute angle is made near the area of interest by means of a sharp needle. The initial nitrocellulose replica is then replicated by a thin double film of beryllium and quartz. This double film is necessary because the final replica is supported by a specimen screen having a large hole in the center to eliminate masking due to specimen screen wires. The first organic film is removed with solvent vapor. The acute angle near the important structure aids in its location and in the interpretation of shadows.
A Centerable Condenser Aperture for the RCA Model B ElecAmerican Viscose Corp., tron Microscope. F. F. MOREHEAD, Marcus Hook, Pa. The alignment of this instrument is simplified by employing a mechanical arrangement for centering the condenser aperture while the instrument is in operation. -4 pair of spring tension ad-
