The first step in NHzCl oxidation of NOz-is the general acid-assisted formation of nitryl chloride, where km is 7.6 X loe M-2 s-l for H30+ and is 46 M-2 s-l for HzP04-(25.0 "C, p = 0.50 M). This is the rate-limiting step at very low [NHJ and high [NOz-I concentrations: HA + NHzCl+ NOz--A-+ NH3 + NOZC1, where the subsequent reactions of NOzCl are rapid. Under conditions of higher [NH,] and lower [NOz-], the overall rate of loss of NHzCl is suppressed, and a complex rate expression is observed. This rate dependence is derived from an analogous mechanism found for the reaction between OC1-and NOz-:. In this mechanism, NOzCl forms reversibly in the first step (k~'/k-l') and either reacts with a second NOz-(kz) to give Nz04 or loses C1-(k4) to give NOz+; both Nz04 and N02+ hydrolyze rapidly to give NO,-. The relative reaction rate of OC1-+ H+ + NO2-is estimated to be 1.8 X 105 greater than for NH2Cl + H+ + NOz-. An equilibrium formation constant, Kf =[NHZC~]/([NHJ[HOC~I) = 3.8 X 1O1O M-l, is calculated from the kinetic data.

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A spectrophotometric method for the determination of molybdenum in steel, based on the colour reaction with thiocyanate in the presence of tin(I1) chloride and a titanium catalyst, has been adapted for the Technicon AutoAnalyzer. The method is suitable for most steels, but small corrections may be needed in the presence of high concentrations of chromium, cobalt and vanadium. Nickel, manganese and silicon a t the usual levels do not interfere. For low-alloy steels the initial solution is identical with that required for an existing automatic method for manganese and phosphorus, but is modified when required to deal with high-speed steels containing alloying additions of tungsten. Results on standard steels are presented, and a statistical survey of long-term reproducibility is given.

Direct-reading optical-emission spectroscopy has been widely adopted in the iron and steel industry as a rapid analytical technique for process control and for other laboratory analyses. The conventional spark stand, however, severely restricts the size and shape of the sample that can be accommodated on the instrument and thus limits the more general use of the technique for on-site analysis outside the laboratory. This disadvantage has now been overcome by using a fibre-optic light-guide to link a mobile excitation head to a conventional spectrometer.Parallel but independent work has been carried out in the authors' laboratories, first on photographic and later on direct-reading spectrometers. A t the Corby laboratories, further work has resulted in the manufacture and application of an inspection analyser that incorporates a 5-m guide. Typical calibration graphs, reproducibilities and examples of material identification are given, and possible applications are discussed.Steel is produced to many different compositional specifications according to its intended usage. During recent years there have been outstanding advances in the analytical procedures used for process control, thus making possible the more economic production of ever higher tonnages of steel of assured composition. In the interval between primary production and the finished product and again before the latter reaches the customer, however, there may be many intermediate stages of manipulation, e.g., forming, sub-division and transportation, at any of which normal identification marks may be obliterated. Although great precautions are taken, loss of identity, with the attendant risk of mix-ups, is a very serious matter and has been of concern to quality control engineers for many years. This problem has led to a continuing quest for rapid and reliable methods for the identification of material on-site.'Generally, purely chemical methods of identification are not well suited to large-scale production, although local spot-testing, for example with dimethylglyoxime for nickel, is sometimes useful. Physical methods, based, for example, on the magnetic or electrical properties of the material, have been more widely applied but, unfortunately, they indicate chemical composition only indirectly and are too easily affected by other metallurgical factors. Other miscellaneous methods include spark testing, and the use of portable isotope analysers and direct-vision spectroscopes. Although each may be helpful in specific circumstances, none meets entirely the requirements of quality control inspection. Equipment that does have the potential for this kind of work is that based on measurement of spectral radiation, either optical or X-ray.Traditionally, however, such equipment, while of excellent use in the laboratory and highly developed in this context, has been unsuitable for on-site quality control inspection, as it is too bulky, fragile and easily upset by vibration or temperature variations. Recent developments by the manufacturers have now enabled sin...

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