<p>The stability and liftoff characteristics of a nitrogen (N₂) diluted hydrogen (H₂) jet flame in a vitiated co-flow are investigated experimentally with particular attention focused on regimes where multiple stabilization mechanisms are active. Information gleaned from this research is instrumental for informing modeling approaches in flame transition situations when both autoignition and flame propagation influence combustion characteristics. Stability regime diagrams which outline the conditions under which the flame is attached, lifted, blown-out, and unsteady are experimentally developed and explored. The lifted regime is further characterized in determining liftoff height dependence on N₂ dilution, jet velocity, and co-flow equivalence ratio (or essentially, co-flow temperature). A strong sensitivity of liftoff height to N₂ dilution, jet velocity, and co-flow equivalence ratio is observed. Liftoff heights predicted by Kalghatgi’s correlation are unable to capture the effects of N₂ dilution on liftoff height for the heated co-flow cases. A uniquely formulated Damköhler number, where the chemical time scale is based on flame propagation rather than autoignition, was therefore developed which acceptably captures the effects of jet velocity, nitrogen dilution and environment temperature on liftoff height. Satisfactory agreement between the correlation results indicate that stabilization is dominated by propagation, and prior studies with similar flames, such as the research of Muñiz and Mungal (1997) indicate that the propagating flame is likely tribrachial.</p>

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Rapid and simple methods are described for the determination of copper, cobalt, nickel, niobium, tantalum, lead and uranium in soil samples. Following the breakdown of the samples and dissolution of the trace metals by methods applicable in the field, the trace metal or metals are separated chromatographically by apward 'diffusion of a solvent on slotted sheets of paper which enable ten separations to be performed simultaneously. The metals are detected by spraying the strips with suitable reagents and the amount present is determined b,y visual comparison with standards. Copper, cobalt and nickel are determined after a single separation. The same soil extract is used for the determination of both niobium and tantalum. This type of prospecting is rapidly growing in popularity and importance. March, 19551 METHODS OF ANALYSIS TO GEOCHEMICAL PROSPECTING 173 * Uranium determined colorirnetrically.

The CO 2 emission prevention advantage of generating power with high hydrogen content fuels using gas turbines motivates an improved understanding of the ignition behavior of hydrogen in premixed and partially premixed environments. Hydrogen rich fueled flame stability is sensitive to operating conditions, including environment pressure, temperature, and jet velocity. Furthermore, when premixed or partially premixed operation is needed for nitric oxide emissions reduction, a diluent, such as nitrogen, is often added in allowing fuel/air mixing prior to combustion. Thus, the concentration of the diluent added is an additional independent variable on which flame stability dependence is needed. The focus of this research is on characterizing the dependence of hydrogen jet flame stability on environment temperature, pressure, jet velocity and diluent concentration by determining the dependence of the liftoff height of lifted flames on these 4 independent parameters. Nitrogen is used as the diluent due to its availability and effectiveness in promoting liftoff. A correlation modeling the liftoff height dependence on operating conditions is developed which emphasizes the factors that bear the greatest impact on ignition behavior.

Geochemical prospecting methods for the determination of trace amounts of tungsten and molybdenum in soils by means of dithiol (toluene-3 : 4-dithiol) are described.The soils are fused with a modified carbonate flux, the melts are leached with water, and aliquots of the aqueous extracts are used for the determinations. At high temperatures (about 100" C) the blue-green tungstendithiol complex is extracted selectively into isoamyl acetate from concentrated hydrochloric acid solutions containing stannous chloride, which prevents the formation of the molybdenum complex. A t low temperatures (20" to 25OC) the yellow-green molybdenumdithiol complex is extracted selectively into isoamyl acetate from dilute hydrochloric acid solutions. Determinations are made by visual comparison of the colour intensities of the dithiol complexes with standards.The field methods, as described, can be used for the determination of tungsten over the range 4 to 400 p.p.m., and molybdenum over the range 1 to 100 p.p.m. in soils. Simple modifications of the methods permit the determination of greater amounts of the trace metals. SOILS, water, stream sediments and plants in the neighbourhood of ore bodies frequently contain high or anomalous amounts of the elements constituting the ore compared with the normal or background values in similar materials in barren regions. This is consequent on the primary geochemical dispersion of the elements at the time of mineralisation, and their subsequent redistribution by physical or mechanical, chemical and biochemical agencies to give secondary dispersions. Geochemical prospecting methods based on the analysis of soils