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
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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.
