Chemical Equivalence Research Articles

Proterozoic continental volcanism in the Belcher Islands: implications for the evolution of the Circum Ungava Fold Belt

The Belcher Islands of eastern Hudson Bay expose a continuous sequence of Early Proterozoic volcanics, and continental and shallow-marine sedimentary rocks. The volcanic rocks comprise two sequences of continental basalts: the older Eskimo Formation and the younger Flaherty Formation. The flows of both formations are composed of tholeiitic basalts (MgO < 9 wt.%) which, in each formation, are divided into two groups based on the concentrations of high field strength elements. Both groups of Eskimo flows have fractionated rare earth element (REE) patterns, with negative Nb anomalies. Relative to Eskimo flows, the Flaherty flows have flatter REE profiles and higher Nb contents. The chemical variations observed in the Eskimo flows are consistent with an assimilation – fractional crystallization process, involving a lower continental crust contaminant. The major and most trace element trends of the Flaherty flows are attributed to gabbroic crystal fractionation of two parental liquids, which are interpreted to represent varying degrees of partial melting of a common mantle source. An increase in La/Sm with increasing La, however, requires that the Flaherty flows evolved under open-system conditions, possibly in a replenished magma chamber or by selective contamination. The interbedding of low- and high-Zr flows in the upper portion of the Flaherty Formation combined with the possibility that their parental magmas originated from a common source require a complex melt segregation process in a partially molten ascending mantle.The chemical compositions of coeval basalts exposed along the eastern Hudson Bay coast and in the Cape Smith Fold Belt (western and eastern Povungnituk Group) indicate that they can be divided into two groups that are the chemical equivalents of the Eskimo and Flaherty Formations. Presently, the chemical stratigraphy of the Belcher Islands offers the most reliable means of correlating the isolated segments of Proterozoic supracrustal volcanics that rim the Superior Province of northern Quebec.

Toluidine Blue Selective Plasticized Poly(vinyl chloride) Membrane Electrode for Colloidal Titration

Abstract A plasticized poly(vinyl chloride) membrane electrode was applicable to colloidal titration without selective substances. The change of potential in the end-point, however, was too small to measure accurately. We prepared a new type of electrode with toluidine blue as an indicator. It was found that the electrode was quite useful to the colloidal titration. At the end-point a large change of potential was observed, and a small amount of polyelectrolyte anion could be titrated directly. Potassium poly(vinyl sulfates) was titrated with errors not more than 0.7% of r.s.d. in the amount of several micro chemical equivalents. This method was used to measure some poly(isoplene sulfonates) used as a dispersant polymer and its results agreed with that of acid-base titration.

Two-group Raman optical activity revisited

In the circular differential Raman scattering observed in biological and other large polyfunctional molecules, many spectral features may be attributed to conferred chirality, in the following sense. Although a given vibrational transition may occur within a group in an intrinsically achiral local environment, it is coupling with another achiral but dissymmetrically placed group that generates the chiral response. Where two groups so coupled are chemically dissimilar, the effect originates in interference between one- and two-centre scattering mechanisms. The one-centre mechanism entails vibrational transition by a group as it undergoes conventional Raman scattering. The two-centre mechanism involves mediation of the chiral influence of a second group on this transition by Förster-type radiationless energy transfer. Where quantum-mechanical interference generates a differential Raman signal, the circular intensity differential depends on the inverse square of the distance between the groups so coupled. This distance dependence may be understood as originating from a combination of two factors. One is the linear distance dependence characterising Raman optical activity due to direct interference between transitions at distinct sites, which arises in the case of chemically identical groups. The other is the inverse cubic distance dependence associated with the probability amplitude for Förster energy migration. The Raman optical activity of any group with no chemical equivalents in its vicinity should thus be interpreted as resulting from a sum of inverse-square couplings with other chromophores. The two-group model for Raman optical activity is critically assessed, possible ways to improve upon the model are considered, and the result for the differential scattering intensity is recast in a new form that is more general and also more consise than has hitherto been presented.

X‐Ray crystallographic study of a 1,3,2‐dioxaphosphorinane dimer containing five‐coordinated phosphorus in the 12‐membered ring

AbstractAttempted preparation of phosphorane 9 with a 1,3,2‐dioxaphosphorinane ring attached diequatorially to phosphorus led to a mixture of products from which was isolated 12‐membered ring phosphorane 10, formally the dimer of 9, in low yield (22%). An X‐ray crystal structure of 10 revealed a highly symmetrical molecule with trigonal bipyramidal geometry at both phosphorus atoms. The 12‐membered ring is attached to phosphorus diequatorially. The ring is strongly puckered about phosphorus with an equatorial O‐P‐O angle of 110°. The chemical shift equivalence of the CH2O resonances in the 1H NMR spectrum of 10 shows the 12‐membered ring to be highly mobile at ambient probe temperature. At −89°C, these resonances are fully decoalesced. The value of ΔG‡ for the process that averages these peaks was found to be 10.1 kcal/mol at coalescence (−42.0°C).

Requiem for an Unknown Leper

To the Editor. —Dr Crawshaw's Requiem for an Unknown Leper1 is a moving description of the stigma of Hansen's disease (leprosy) and how this stigma and so-called treatment amplified the suffering of those ill with the disease. It closes with a strong plea for physicians not to be numb to the experience of their patients. As a practicing psychiatrist, I can hardly quarrel with this. But as a practicing psychiatrist, I find the essay marred by apparently uninformed criticisms of ECT, referred to as shock therapy. Crawshaw states that electroshock treatment is iatrogenic numbness, and that we should First do no harm with our mind-numbing tests, procedures, and pharmacopeia, the chemical equivalent of electroshock. I don't know what specialty Crawshaw practices, but I doubt that it is psychiatry, since contact with the current clinical use of ECT should dispel the popular but erroneous myth that the procedure somehow damages brains

Differences in Nitrogen and Mineral Contents in the Kernels of Cerals, Buckwheats and Pulses.

イネ科, タデ科, マメ科作杓(イネ, ヒエ, アワ, キビ, 食用モロコシ, 飼料用モロコシ, ハトムギ, コムギ, オオムギ, ソバ, アズキ, インゲンマメ, ダイズ)の穀粒を供試し, 合計719点の試料について, そのN, P, K, Mg, Ca, Mnの含量を分析調査した. その結果, 東アジアで伝統的に食用として重んじられてきたイネ科およびタデ科作物の穀粒は, Mg/K化学当量比が1.5付近にあって, いずれもMgに富む品質特性を示すことを見出だした. また西アジア起源のムギ類などの穀粒はMg/K比が1.0付近にあって, KとMgがほぼ等量含まれていた. マメ科作物の穀粒はNとKにすこぶる富む点が特徴的であった. すなわち, 穀粒のK, Mg含量やMg/K比は作物種ないし品種群ごとに一定の範囲に収束する傾向を示すところから, これは遺伝的特性の影響が最も大と考察された. このほか施肥あるいは栽培条件などの差によると見られる品種内変動も観察されたが, これらの点については, さらに詳細な実験結果を待って結論を得る必要があるものと考えられた.

Comparison of solid‐state and solution structures of (R3P)2CdX2, (Et3P)2Cd2X4 and (Bu3P)3Cd2X4 complexes

AbstractThe cadmíum (II) phosphine complexes (Et3P)2Cd2X4, (R3P)2CdX2 [R3P = Ph3,P, Bu3P, Et3P, 1‐phenyldibenzophosphole (DBP), and 1‐phenyl‐3,4,‐dimethylphosphole (DMPP)] and (Bu3P)3Cd2X4 (X = Cl, Br, I) have been prepared and their solution and solid state structures determined by a combination of elemental analyses, conductance, infrared and NMR spectroscopy. The structures of (Ph3P)2CdI2 (1) and (DBP)2CdI2 (2) have been determined from three‐dimensional X‐ray data collected by counter methods. Compound 1 crystallized in space group P21,/a with a = 18.312 (9), b = 10.285 (5), c = 19.311 (9) Å, β = 115.53 (4)° and Z = 4. Compound 2 crystallized in space group P21,/n with a = 12.698 (3), b = 15.302 (4), c = 17.477 (4) Å, β = 96.66 (2)° and Z = 4. The structures were refined by least‐squares methods with RF = 0.041 and 0.048 for 4157 and 3393 unique reflections with I/σ(I) ⩾ 2.0 for 1 and 2, respectively. Both molecules deviate from ideal C2v symmetry and have very slightly different Cd‐I (1; 2.724 (2), 2.731 (2); 2; 2.718 (1), 2.721 (1) Å) and Cd‐P (1, 2.631 (2), 2.653 (2); 2; 2.616 (3), 2.603 (3) Å) bond distances. The Cd‐P bond distance differences are sufficient to give rise to a second order ABX CP/MAS 31P{1H} NMR spectrum for 1 but for 2 the phosphorus nuclei of the two DBP ligands are chemical shift equivalent. The CP/MAS 113Cd{1H} NMR spectra of both compounds 1 and 2 show apparent first order triplets. The (Bu3P)3Cd2X4 complexes are shown by variable temperature 31P{1H} NMR and conductance measurements to exist in solution as equilibrium mixtures of (Bu3P)2Cd2X4 and (Bu3P)2CdX2. CP/MAS 31P{1H} and 113Cd{1H} NMR spectra suggest that these compounds exist as doubly halide bridged (R3P)2Cd(μ‐X)2CdX2(R3P) species containing four‐ and five‐coordinate cadmium in the solid state. Equilibrium and activation thermodynamics for the ligand exchange processes of representative complexes have been determined from variable temperature 31P{1H} NMR spectra in CDCl3/CH2Cl2 (1:1) solutions.

Haze and other aerosol components in late winter Arctic Alaska, 1986

Three coarse and five fine aerosol components of different elemental compositions were identified at Barrow, Alaska, from March 17 to April 21, 1986, resolved by absolute principal component analyses of element concentrations in 280 sequential coarse and fine size fraction time step samples. In the coarse (> 2.5 μm), two components C‐1 and C‐2 had abundant Si, S, Cl, K, and Ca, but no Al, and together contained 85% of coarse S. Their compositions resembled expected products of carbonaceous fuel combustion, with Si being volatilized by carbon reduction and other metals volatilized perhaps as chloride salts. C‐1, with high trace metal contents, might be from nonferrous smelting, whereas C‐2, with high Fe, might be associated with conventional coal combustion. Both appeared semi‐aged with respect to acidic gas uptake because the S chemical equivalents were less than those of metals contributing to alkalinity. When combined with Cl, S was close to the metal equivalents, indicating complete acid‐base titration. A strong concentration rise of C‐1 and C‐2 occurred from March 25 to April 2 during a haze event, although C‐1 was also present at other times. Air trajectories showed that air masses arrived at Barrow during the haze event from eastern or northern Europe. The third component C‐3 was a dust aerosol rich in Al that contained high S but low Cl, suggesting saturation with H2SO4 and therefore aged and regional aerosols perhaps typical of the late winter Arctic. No major change in its concentration was observed to correspond to synoptic events. In the fine (< 2.5 μm), five components represent a sea‐salt aerosol, an S‐rich aerosol with some Si, K, Ca, and Fe, a trace metal aerosol, an Al‐rich dust, and a marine product with Br, S, and Cl. The sea‐salt was found only in three plumes when synoptic meteorology and air trajectories suggested origins in the North Pacific. The S‐rich aerosol, accounting for 73% of S and 40% of Si, was enhanced during the haze event by 75%, and existed over the entire period at rather high levels and might be due to SO2 oxidation and condensation on fine Si‐rich particles. The trace metal aerosol was always present and could have been generated from nonferrous smelters at lower latitudes. The Al‐rich dust particles contained 7% of S and were similar to component C‐3. The marine aerosol contained 74% of Br, 69% of Cl, and 20% of S, and could be from oxidation of marine biogenic Br and S gases. All but the sea‐salt were present at Barrow throughout the period, with no clear relation to air trajectories or synoptic meteorology. The results show that certain winter meteorological conditions favor pollutant transport from lower latitudes to the Arctic. But while haze is related to industrial pollutants, other nonpollution products are present in the winter Arctic and may be important constituents of haze. They also show that by careful data reduction and meteorological analysis, the sources and transport pathways of haze may be better understood.

Chemical equivalents in metrological support to air-quality analyzers

Chemical equivalents in metrological support to air-quality analyzers

Experimental investigation of electrostatic fire accidents after aircraft landing and preventive measures

This work is an experimental investigation to determine the cause of electrostatic fire accidents after aircraft landing and to clarify the effects of various factors on the cause. This research work has conducted a series of ground simulation tests and actual flight tests under the fire and explosion environment conditions. The test results have indicated that the process of an aircraft landing run is the fundamental process of electrostatic charges generating in fuel tanks. After an aircraft comes to a stop, there is also a process of accumulation of electrostatic charges, while fuel charged with higher energy remains for a considerably long period, unable to dissipate. All kinds of unbonded conductors in the tank are electrodes for dangerous spark discharges. When an aircraft using RP-2 fuel flies in hot weather, the concentration of flammable vapor produced in the space above the fuel surface inside of the tank will, under certain conditions, come close to its chemical equivalent, thus possessing the condition of combustibles under which an electrostatic spark can cause fires and explosions. Some principles that should be followed in aircraft fuel system design are discussed.

Chemical equivalence of two polyetherpolyurethane foams as a vehicle for povidone—iodine solution: Kinetic model for the loss of available iodine

The loss of available iodine from povidone—iodine solution stored in contact with two different polyetherpolyurethane foams was monitored as a function of time and temperature. Statistical evaluation of the results for the four temperatures studied [ambient (25°), 30, 45 and 55°C] indicated the chemical equivalence of the two foams as storage and delivery systems for povidone—iodine solution in terms of solution stability. In addition, application of a first-order kinetic model to the data produced an acceptable fit. An Arrhenius-type evaluation of the resulting rate constants yielded a linear relationship which was shown to be useful for predicting loss of available iodine under ambient temperature conditions of storage.

Synthesis of 1,3-dioxin-4-ones and their use in synthesis. XVI. 4-Oxo-1,3-dioxin-5-carboxylic acids and related compounds: Versatile synthetic intermediates for the synthesis of 6-unsubstituted six-membered heterocyclic compounds.

A novel method for the synthesis of so far unknown 1, 3-dioxin-4-ones having a carboxyl group at the 5-position is described. Reaction of formyl Meldrum's acid and an alcohol in an aprotic solvent at 50-60°C gave the corresponding half esters of formylmalonic acid. Treatment of the latter with appropriate ketones in acetic anhydride containing a catalytic amount of p-toluenesulfonic acid gave the desired dioxinone-5-carboxylates.Successful conversion of these 1, 3-dioxin-4-ones either to 1, 3-oxazine-2, 4-dione or uracil derivatives having an alkoxycarbonyl group at the 5-position demonstated that these dioxinones can serve as chemical equivalents for alkoxycarbonylformylketenes.The fact that 5-benzyloxycarbonyl-1, 3-dioxin-4-one can readily be transformed to the so far unknown 5-aminodioxinone derivative indicates further the importance of the dioxinone having a carboxyl group at the 5-position as a new building block for heterocyclic compounds.

Chemical Equivalence of Phosphoenzyme Reaction States in the Catalytic Mechanism of the Red Beet (Beta vulgaris L.) Plasma Membrane ATPase

A comparison of two phosphoryl enzyme reaction states associated with the plasma membrane ATPase of red beet (Beta vulgaris L.) storage tissue was carried out to determine if their differences in reactivity toward ADP and K(+) was related to a structural difference in the site of phosphorylation. Using a pulse labeling method it was possible to produce preparations where either the ADP-sensitive and -insensitive phosphoenzyme forms or the ADP-insensitive phosphoenzyme form alone were trapped as trichloroacetic acid denatured protein. Following complete digestion with Pronase, both preparations yielded radioactive tripeptides with similar properties with respect to pH stability of the covalent bond linking the phosphate to the peptide, isoelectric point, and migration on cellulose thin layer plates. Since the preparation containing both intermediate reaction states behaved in a uniform manner during analysis and displayed properties similar to the preparation containing only the ADP-insensitive phosphoenzyme form, it was proposed that both phosphoenzyme forms were chemically equivalent and derived from the same region of the catalytic active site. The observation that ethyleneimine treatment of both preparations followed by trypsin digestion resulted in the production of tripeptides similar to the Pronase fragments would support this proposal since it suggests that the tripeptides from both phosphoenyzme states contain a lysine residue on the C terminal end and are adjacent to a cysteine residue on the N-terminal end. The chemical equivalence of these two phosphoenzyme reaction states suggests that their differences in reactivity toward ligands may be related to conformational changes associated with the catalytic and transport mechanism of this enzyme.

NMR in chemically exchanging systems. Is the number of sites equal to the number of frequencies?

In the treatment of the NMR spectra of multisite exchanging systems, it is sometimes possible to reduce the dimension of matrices by using the fact that some of the sites are equivalent. However, the existence of identical spin Hamiltonians at some of the sites is found to be insufficient in general for simplification of the problem: The symmetry of the exchange network linking the sites must be considered too. Some cases in solid-state and liquid-state NMR are examined. The conditions for simplification of multisite exchange problems are compared with the distinctions between chemical and magnetic equivalence in the high-resolution NMR of coupled spin systems.

Problems in the recognition of seawater intrusion by chemical means: an example of apparent chemical equivalence : Tellam, J H; Lloyd J.W Q J Engng Geol V19, N4, 1986, P389–398

Problems in the recognition of seawater intrusion by chemical means: an example of apparent chemical equivalence : Tellam, J H; Lloyd J.W Q J Engng Geol V19, N4, 1986, P389–398

Composition of the Cayley formation at Apollo 16 as inferred from impact melt splashes

Chemical data for impact melt splashes (IMS) collected at the Apollo 16 landing site show that Ni concentrations and FeO‐Ni, Cr‐Ni, and Co‐Ni correlations are consistent with a chondritic meteoritic component present at levels between approximately 1.5 and 11 wt %. Like Apollo 16 soils, the IMS are intermediate in composition to Apollo 16 rocks. The chemical data for the IMS are consistent with two main compositional groups. The Group A IMS (28 samples) are chemically distinct from local Apollo 16 soils and are very similar to mixtures of anorthosite and low‐Sc VHA (LScVHA) impact melt rocks. Calculated to a meteorite‐free basis, their average Sc concentration, La/Sc, MgO/Sc, and TiO2/MgO ratios, and mg′ value are 6.1 ug/g, 1.94, 9800, 0.066, and 0.74, respectively. The Group B IMS (seven samples) have chemical equivalents among the soils. Five samples are chemically very similar to mature Apollo 16 soils from the central and southern parts of the landing site; two are more similar to soils 67601 and 67941 from North Ray Crater. Generally, the Group B IMS and soils are enriched in a composition similar to anorthositic norite (67215) or mixtures thereof with anorthosite as compared to the Group A IMS. The average Sc concentration, La/Sc, MgO, and TiO2/MgO ratios, and mg′ value for the subgroup of five are 9.3 ug/g, 1.41, 5780, 0.124, and 0.66, respectively. The corresponding values for the subgroup of two are 7.5 ug/g, 1.04, 7400, 0.090, and 0.71, respectively. The Group B IMS (and most soils) have a minor high‐Ti component not present in the Group A IMS. If this component is high‐Ti mare basalt, its average concentration is approximately 1.6 wt %. The seven Group A IMS that have been dated by rare gas methods all have approximately 2 m.y. exposure ages, an age generally associated with South Ray Crater. These seven and potentially most Group A IMS are likely quenched samples of the melt volume produced by the South Ray impact. The chemical signature of the impacting projectile is chondritic, and its average concentration for the Group A IMS is 7.3 wt %. Like large, coherent melt sheets from terrestrial impacts, the impact melt volume of the South Ray impact as represented by the Group A IMS is homogeneous with respect to target lithologies. Target lithologies at South Ray Crater, which are represented by the host rocks for the IMS, include anorthosite, LScVHA impact melt rocks, HScVHA impact melt rocks, and dimict breccias. With the exception of 61016, the melt portion of analyzed dimict breccias has the HScVHA composition, implying that the dimensional scales of LScVHA‐type of rocks and anorthosite in the South Ray target do not extend to the 1–10 cm scale observed for the HScVHA dimict breccias. The compositional difference between Group A IMS and surface soils from the southern part of the landing site implies stratigraphic variation in the dominant type of VHA impact melt rock within the Cayley Formation. Chemical data and mixing‐model results are consistent with a model in which HScVHA rocks dominate LScVHA rocks in the surface layer. The LScVHA rocks dominate HScVHA rocks in the layer beneath. The South Ray impact penetrated both layers, as both types of VHA impact melt rocks are traceable as ejecta material. Its impact melt volume was formed primarily from the lower layer to give the observed composition of the Group A IMS. That the North Ray impact also sampled the lower layer is indicated by the chemical affinities of soils 67601 and 67941 with the LScVHA composition. Away from North Ray Crater, most soils have chemical affinities with the HScVHA composition, reflecting soil development primarily from the surface layer. Estimated average compositions give TiO2, MgO, Sc, and La concentrations of 0.69 and 7.1 wt % and 10.5 and 21.2 ug/g, respectively, for the surface Cayley layer and 0.38 and 5.9 wt % and 6.1 and 11.8 ug/g, respectively, for the subsurface Cayley layer. An average composition estimated for the Descartes Formation from soil compositions has TiO2, MgO, Sc, and La concentrations of 0.25 and 3.5 wt % and 7.7 and 2.2 ug/g, respectively. The Cayley Formation is more KREEPy, more magnesian, and less aluminous than the Descartes Formation.

Problems in the recognition of seawater intrusion by chemical means: an example of apparent chemical equivalence

Summary The determination of the origin of saline groundwaters is sometimes crucial for the successful exploitation of an aquifer system. Although hydrochemical methods provide a direct approach to the problem, modification of intruding water can often give rise to interpretational difficulties. By means of a case history from the Permo-Triassic sandstone aquifer of the Widnes-Manchester area, the problems encountered are illustrated. The major ion chemistries of (a) saline waters originating from upconing of deep old saline water and (b) saline groundwaters resulting from recent intrusion are compared using computer modelling techniques with a third group of waters of unknown provenance. It is concluded that in some cases an apparent chemical equivalence, in which the same chemical product can arise through more than one set of processes, can occur; in such cases major ion analyses alone are not of use in determining groundwater origins. Explicit discussion of equivalence problems has rarely been undertaken in the hydrochemical literature, and the results presented have implications beyond saline intrusion studies.

Geochemical aspects of granite and related rocks

Report of a meeting held in Burlington House on 28 November 1985. The meeting was convened by K. Coe, and chaired by W. S. Pitcher and M. Brown, morning and afternoon sessions respectively. A special scientific meeting of the Society was held on Thursday 28 November 1985, with the title Geochemical aspects aspects of granite and related rocks. From the papers offered, ten were selected which dealt with data and concepts derived from British and Irish granitic bodies. One exception to this was the first contribution, presented by R. Macdonald. In this it was proposed that because of late crystallization and subsolidus processes, plutonic granites may not record magmatic chemistry. Macdonald and his co-workers suggested that silicic obsidians, rhyolites and acid ash-flow sheets may be better indicators of original composition, implying that these extruded rocks are the chemical equivalents of unmodified granitic liquids. This precept was used in interpreting data derived mainly from the Western Cordillera to show that compositions of source rocks were in some cases more important than the tectonic setting of the magma. The second paper, by D. A. C. Manning , emphasized the importance of the volatiles B, F, Li and P in granites, manifest in familiar ‘accessory’ minerals and exerting controls on various aspects of the melt, including its emplacement mechanism. Other trace and some major element abundances correlated with these indicating a genetic relationship. A lower crust source for the volatiles was suggested. Two papers followed on the younger and older granites of the

Synthesis of 1,3-dioxin-4-ones and their use in synthesis. XIII Synthesis of 5-halo-1,3-dioxin-4-ones and their conversion to 5-alkyl derivatives.

A novel method for the introduction of an alkyl group at the 5-position of 1, 3-dioxin-4-ones is described. Reaction of 5, 6-unsubstituted 1, 3-dioxin-4-ones with N-halosuccinimide in acetic acid followed by treatment with a base gave 5-bromo- and 5-iodo-1, 3-dioxin-4-ones, which were converted to the corresponding 5-alkylated dioxinones either by palladium-catalyzed cross-coupling or by photochemical allylation reactions. Successful conversion of 5-ethyl-2, 2-dimethyl-1, 3-dioxin-4-one either to a 5-ethyl-1, 3-oxazin-4-one derivative or an α-ethylformylacetate upon heating in xylene demonstrated that these 5-substituted 1, 3-dioxin-4-ones can serve as chemical equivalents for substituted formylketenes.

Stabilization Mechanism of Turbulent Wake Flame Behind Bluff Bodies with Fuel Injection : 1st Report, Blow-off Limits

Stability of wake flames formed behind a bluff-body with fuel injection was investigated experimentally in various geometries of two-dimensional bluff-bodies such as cylinders with 10-20mm diameters, hemi-circle, 60°wedge and rectangular rods of 12.5mm width. The bluff-body was located in an air stream flowing 5-60m/s. Fuels used were propane, methane, ethylene and butane. Flame stability limits, length or geometry of recirculation zone, distribution of chemical species concentrations, temperature and equivalence ratio in the zone were measured. The results show that the equivalence ratio in the recirculation zone is important in determining the flame limit. The air velocity at blow-off is inversely proportional to the square root of the bluff-body width, and is independent of the direction of fuel injection and the geometry of flame holder except for the rectangular rod.