Separation of Zirconium from Hafnium. Hafnium and zirconium, ordinarily very difficult to distinguish chemically, can now be separated by a single-step anion-exchange process. The separation for analysis is obtained by using a strong quaternary-amine anion-exchange resin column with diluted sulfuric acid as eluting solution. After separation of a mixture containing approximately 100 mg each of hafnium and zirconium, a spectrochemical examination showed only a few ppm (parts per million) cross contamination.

The method results from a systematic study of the elution behavior of a variety of zirconium and hafnium complexes. It is better adapted to the examination of hafnium-base alloys, because the hafnium is removed first in the elution cycle, and less trouble is encountered in the hydrolysis of ions of this element. In connection with this work, a procedure was developed for the quantitative analysis of zirconium in hafnium metal, which is used as a control-rod material in nuclear reactors.

Distillation Techniques Improved. Vapor-liquid chromatograms resulting from successive fractions of precise laboratory distillations are generally more informative than the boiling temperatures or the refractive indices because the progress in constituent separation is usually clearly shown. The method is now being used routinely in the distillation laboratory with improved results.

A new and better procedure for maintaining a constant flow of vapor to the column of a laboratory still was developed. Control of this vapor velocity is important because better separations of materials are obtained when the velocity is low but constant. The method depends on the use of a thermistor as a flowmeter to control the heat supplied to the vaporizer of the still. This process has a number of advantages over the usual method of controlling the heat supply by the changes in the vaporizer pressure.

A simple and reliable method was developed for cooling the reflux heads of laboratory stills to low temperatures. With this technique, the low temperatures may be maintained for long periods of time.

Accuracy for pH Standards Increased. Measurements of the acidity or basicity of solutions, expressed on the pH scale, are of far-reaching importance in chemical analysis, medical research, and modern industry. Because control of the pH is essential in many industrial processes, some years ago the Bureau took the lead in establishing a standard pH scale which would meet the practical needs of industry and possess, as well, the fundamental meaning demanded by science. Although standards for the adjustment of pH-measuring equipment have been issued by the Bureau for more than 15 years, fundamental difficulties in the calculation of a standard pH have made it necessary to limit the accuracy in the assignment of standard pH values to ±0.01 unit. However, during the past year, a mutually satisfactory convention was developed in cooperation with the pH committee of the British Standards Institution, and the third decimal place is now being assigned to pH standard values.

A Standard for Blood pH. To discover the relationships that exist among physiological function, pathological condition, and pH, medical and biological laboratories have long studied the acid-base relationships in blood and other physiological fluids. Because blood is a well-buffered fluid, the changes in pH are very small and must be detected with precise pH-measuring equipment. To increase the accuracy with which these measurements can be made, the Bureau established a pH standard for determining the pH of blood and other physiological media with a pH of 7.382 at 37 °C (98.6 °F). The new standard, a mixture of phosphate salts, can be prepared from pH standard materials already issued by the Bureau.

Standard Hydrocarbon Blends. Eight standard hydrocarbon blends are now available from the Bureau for calibrating instruments used in analyzing gasoline and blending stocks. These standard samples primarily intended for mass spectrometer calibration are mixtures containing seven or eight pure hydrocarbons representing C, and C. paraffins and cycloparaffins in typical virgin and catalytically cracked naphthas. The standards may also be applicable for infrared and gas chromatographic techniques. The development of this new group of standard materials is part of an extensive and continual Bureau program to provide standard substances for chemical and physical uses.

Preparative Scale Chromatography. During the past decade, vaporliquid chromatography has developed into an effective and widely used method of separating mixtures. Although it was utilized chiefly for analysis, its use in preparing small amounts of pure materials gradually expanded. As part of a program to extend the applicability of this method to routine purification, a process for automatically injecting samples and "cutting out peaks" to reject undesirable substances was devised. That is, to purify a specimen, any component which has a peak different from the characteristic peak of the specimen is automatically directed to a trap instead of the main ampoule. With these innovations, the chromatographic apparatus will operate automatically for long periods.

Additional improvements are being designed for preparative scale chromatography. Because purification of small amounts of samples is more effective in columns of relatively small capacity than that of large samples in large-diameter columns, the automatic cyclic operation of small to intermediate-size columns was chosen for further development.

Round-Robin Purity Determinations. Although any program directed toward the preparation of pure materials is completely dependent upon procedures for determining purity, the methods of gaging extent of contamination unfortunately do not have the necessary reliability. To obtain the best techniques for such a determination, a committee from the Bureau organized an international cooperative study several years ago of those techniques for determining purity which depend upon freezing-point depression by impurities. Four groups of samples were prepared under conditions designed to assure uniformity and verifiable purity. These speci

mens were issued to 20 leading laboratories in six countries, including the Bureau.

During the past year, the round-robin results that became available demonstrated that accurate results can be achieved by this method. However, they also show that the sources of error are not always understood. From the results, the most effective processes for determining purity were found to be those in which changes in volume, heat content, or control of

Eight new standard hydrocarbon blends were issued for calibrating instruments used to analyze gasoline and blending stocks. Ampoules are filled in a controlled atmosphere with sufficient blend for one calibration (page 75).

the rate of freezing or melting were employed to judge the proportion of a sample which was in the liquid state at any temperature.

Crystal Chemistry. Research on crystal chemistry was expanded to obtain fundamental data on the formation, transformation, and purification of crystalline chemicals in terms of molecular structure. As all physical and chemical properties of solids are ultimately dependent upon structure, it is necessary to understand the relationship between structure and behavior of materials.

During the past year methods were evaluated for automatically recording precise single crystal X-ray diffraction intensities, for deriving the approximate atomic structure of crystals from X-ray diffraction data, for obtaining "flash" X-ray data from transient phenomena and for recording defects in high-purity crystals.

Three types of investigations were continued on purification by singlecrystal growth: formation of pure single crystals, retention of impurities, and effect of defect structure on the properties of crystals.

Coordination Chemistry. Both theoretical and practical interest in the field of coordination compounds has increased in recent years because of the unusual properties that these compounds exhibit. Through coordination with suitable complexing agents many metal ions can be either activated or deactivated. In addition, many of the coordination compounds were shown to be useful catalysts whereas others were found to exist as intermediates in reactions. To study the preparation, stability, and mechanism and kinetics of formation of such compounds, the Bureau began an investigation of coordination compounds of the first transition metal series. The structure of these compounds is being studied with resonance spectroscopy and X-ray diffraction techniques.

Radiochemistry. Considerable effort was devoted to designing a new radiochemical facility for conducting fundamental investigations in radiochemical methods and for applying modern radiochemical techniques to existing research problems. By detecting tracer atoms and measuring the energy released from artificially radioactive species, the Bureau will study mechanisms of chemical processes and develop sensitive analytical methods. As part of this program, the analysis of trace constituents by neutron activation analysis will be stressed.

2.2.2. PHYSICAL CHEMISTRY

In response to the demand for more detailed information on the structure of molecules and elementary molecular processes, the Bureau initiated a program to consolidate and strengthen fundamental research on bulk properties of materials and macroscopic physicochemical processes. In the basic experimental phase of this program, special instrumentation was developed and precise data obtained on a wide variety of stable and short-lived molecular species and systems. An associated phase of theoretical research was begun to develop a coherent theory of molecular structure in relation to specific molecular reactivity.

Research activities during the year include the elementary chemistry involved in the synthesis of specially labeled compounds, in the processes induced by radiation and particle-impact, and in the reactions at surfaces. In addition, the structural and electronic parameters of relatively simple stable and transient molecules were determined and special apparatus was designed to measure relative isotope abundances for heavy elements, field emission and ionization at surfaces, reactions at very low temperatures, and fast reactions in transient complex systems.

Reactions of Atoms at Low Temperature. Chemical reactions between very reactive materials normally proceed extremely rapidly. By lowering the temperature at which these processes occur, it is possible to slow down the rate of reaction and thus make observations-for example, energies of activitations which are difficult to make at higher temperature. Through recently developed techniques used in low-temperature research, chemical reactions with low activitation energies can now be studied. The virtual elimination of many secondary reactions at temperatures below 100 °K simplifies the interpretation of kinetic data and permits an accurate determination of kinetic parameters.

In NBS studies, hydrogen atoms were found to react with oxygen at 20 °K, with olefins at 77 °K, and with halogens at 90 °K. The primary reaction products are free radicals which have transient existence and subsequently dimerize and disproportionate to form stable compounds. The primary addition-reaction of hydrogen atoms to propylene was studied in detail and the activitation energy for this process was determined. At present, the effect of substituents on the addition of hydrogen to substituted olefins is being investigated.

Gas-solid Reactions at High Temperature. The failure of metals at high temperatures caused by corrosive attack of hot gases is often a limiting factor in the advancement of high-temperature technology. Because physical and chemical data relating to these phenomena are often lacking, the Bureau is conducting research on various aspects of high-temperature gas-solid interactions at the request of the Atomic Energy Commission. To facilitate this research, special equipment for molecular-beam studies was developed. By using the molecular beam, the reaction between chlorine atoms and a polycrystalline surface of nickel heated to temperatures between 1,100 and 1,600 °K was extensively investigated. Based on this study, the relative reactivities of different crystal planes of copper and nickel to halogens are being determined.

Light Elements. Data on the thermodynamic properties of light elements are essential for evaluating compounds composed of these elements as potential high-energy fuels. To obtain such data, the Bureau is conducting a comprehensive interdisciplinary program of experimental and theoretical work on light elements. For this research, which is under the joint sponsorship of the Atomic Energy Commission and the Department of Defense, "best" values were selected for the heats of formations of a variety of