Silver Carrier Research Articles

Isotope and trace element compositions of silver-bearing ores in the Balkans as possible metal sources in antiquity

Ore deposits in the Balkan Peninsula were intensively mined for silver and other metals in the Roman and medieval periods. Coinage mainly issued by tribal groups between the early 5th and the end of the 3rd century BCE provides indirect evidence that silver extraction predates the Roman conquest of the region. However, identification of centers of past metal production and reconstruction of large-scale silver fluxes can only be achieved using a comprehensive geochemical database of potential ores. Here, we present high-precision Pb–Ag–S isotope data and trace element systematics for 128 ore samples from 36 mineralizations from the Balkans as well as one semi-reacted ore from a settlement site (=archaeological sample) and one andesite analyzed as a whole-rock and as a K-feldspar separate. Each ore site was selected for its geological characteristics and documented or assumed historical and/or archaeological significance.The reported data reconstruct the formation of ore bodies from large pre-existing Pb stocks derived from upper crustal sources, modified by tectonic and metasomatic processes, and eventually remobilized by magmatic activity. Lead isotope maps establish distinct isotopic domains which are linked to geological characteristics and enable an enhanced assessment of potential metal sources in provenance studies. Silver isotopes underscore the importance of hypogene ores of hydrothermal origin comprising galena or sulfosalt minerals as the main silver carrier phases and they can circumscribe ore deposits to those actually used as bullion sources of ancient coinage. We show that the Ag isotope signatures and the silver content of the argentiferous galena-rich ores in the Kopaonik and Zletovo districts (Serbia, Kosovo, and North Macedonia), combined with field evidence for historical metal production and geographical considerations, make them the most likely sources of silver which could have been used for coinage issued by mints in the interior of the Balkans.

Calcium carbonate as silver carrier in composite materials obtained in green seaweed extract with topical applications

Two new Ag–AgCl/CaCO3 composite materials, with different molar ratios Ag:CaCO3, were obtained in a green seaweed (Ulva lactuca) extract by a two steps synthesis. The first step consists in a green, partial reduction of Ag(I) in order to obtain Ag–AgCl crystals, which are deposited in the second step on CaCO3. The composites were characterized by XRD, SEM, EDX, UV–vis, and FTIR spectroscopy. The morphology of composite materials consists in aggregates of calcite nanoparticles, decorated with Ag–AgCl, and the aggregates shape depends on the Ag(I):Ca(II) initial molar ratio. The aggregates are also capped with phytochemicals from green seaweeds, mainly polysaccharides. The composites can be used as a model for the utilization of calcium carbonate as silver carrier in medical applications. The dermatological properties of composites were tested in vivo for healing of burns. An accelerated healing was noticed for the composite with higher silver content. The promising results obtained in vivo recommend the Ag–AgCl/CaCO3 composites for topical applications.

Silver‐loaded delaminated hectorite nanoparticles for antibacterial materials

Silver nanoparticles are excellent antibacterial materials with wide application. However, it is extremely unstable associated with easy aggregation and colour changes. Although a great number of carriers have been developed for stable silver nanoparticles, it is never ending to broaden silver carrier to meet varying applications. Herein, delaminated hectorite was developed as an alternative silver carrier. The structure of silver-loaded delaminated hectorite was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy/energy-dispersive X-ray studies. Silver (8.69 wt%) was loaded onto the hectorite nanoparticles by cationic ionic change and surface coating. The silver-loaded hectorite showed fast bacterial killing ability (kill more than 94% Escherichia coli and 83% Staphylococcus aureus at 50 ppm within 1 h) by destroying bacterial cell wall.

Gold behavior in intermediate sulfidation epithermal systems: A case study from the Zhengguang gold deposit, Heilongjiang Province, NE-China

The Zhengguang gold deposit, a typical intermediate-sulfidation epithermal deposit, is located in the southeastern part of the Duobaoshan orefield, west of the Hegenshan-Heihe suture zone, in the eastern part of the Central Asian Orogenic Belt. The deposit comprises five ore zones with total Au reserves exceeding 35 tonnes, with potential additional resources at depth. All vein-type orebodies are hosted by Paleozoic volcanic rocks and comprise multiple vein sets 1–100 cm in thickness. Although gold generally occurs in native form, or as electrum in epithermal deposits like Zhengguang, both pyrite and sphalerite are known to accommodate modest concentrations of invisible gold. This study employs a combination of petrography and sulfide chemistry to determine the role of invisible gold in the Zhengguang ores and the mechanisms of gold incorporation into epithermal sulfides. Three sulfide stages are identified: an early quartz + pyrite (Py1a, Py1b) ± chalcopyrite (Ccp1) stage; a subsequent quartz + sphalerite (Sph2a, Sph2b) + pyrite (Py2a, Py2b, Py2c, Py2d) + chalcopyrite (Ccp2a, Ccp2b) ± galena ± calcite stage; and a late stage containing deformed quartz + pyrite (Py3a, Py3b) ± sphalerite. Petrography and sulfide chemistry allow three groups of pyrite (Au-poor, Au-rich, and a distinct Sb-rich group) to be distinguished, alongside three groups of chalcopyrite (Bi-rich, intermediate-Bi, and Bi-poor), and two groups of sphalerite (Au-poor, Au-rich). A potential porphyry system is indicated beneath the epithermal system by the appearance of Au-poor pyrite and Bi-poor chalcopyrite. After precipitation of early Au-poor sulfides, inflow of relatively low temperature epithermal fluids led to alteration and replacement of early porphyry-related sulfides, and to precipitation of Au-rich pyrite, Bi-rich and intermediate-Bi chalcopyrite, and sphalerite. Gold-rich pyrite contains up to 140 ppm Au, interpreted as both as lattice-scale substitution (Au1+) and as included particles of native gold (Au0). Epithermal chalcopyrite is an important silver carrier but, although Au is measurable, it is a not a good carrier for gold. A strong positive correlation between Au and Cu in pyrite from the first two stages indicate that gold and other metals were likely sourced from magma-derived hydrothermal fluids. The deposit was formed in the Early Paleozoic but some gold ores appear deformed and partially destroyed by a later metamorphic event during which a distinct Sb-rich pyrite crystallized. This study should catalyze exploration in the orefield as it provides further support for an as-yet undiscovered porphyry system close to the Zhengguang deposit.

Biosynthesis of silver nanoparticles by fungi and their antibacterial activity

Nanotechnology is fast advancing and has currently become more effective than the conventional technologies used in water treatment for unconventional water supply sources. Fungi are more versatile in growth and metal tolerance in contrast to bacterial population. This work aims to achieve fourfold objectives: (1) demonstrate the extracellular synthesis of silver nanoparticle by using two filamentous fungi Penicillium citreonigrum Dierckx and Scopulariopsis brumptii Salvanet-Duval, isolated from east of Lake Burullus; (2) demonstrate the biosynthesized nano-silver particles by UV–visible absorption spectroscopy and transmission electron microscopy. The functional group of protein molecules surrounding silver nanoparticles was identified using Fourier transform infrared analysis; (3) check the antibacterial activity of biosynthesized silver nanoparticles at two concentrations (550.7 and 676.9 mg/l) and interact it with bacteria for different durations (15, 60 and 120 min); (4) use the polyurethane foam as silver carrier and nano-silver solution for the removal of pathogenic bacteria in polluted water. The synthesized silver nanoparticles showed an excellent antibacterial property on gram-positive and gram-negative bacterial strains.

Functional Ag‐Exchanged Zeolites as Biocide Agents

AbstractMaterials based on silver are used for controlling different pathogenic microorganisms. However, the influence of the silver carrier in the biocidal activity of the material has been scarcely reported. The present research is focused on studying the influence of zeolite properties on the biocidal activity of silver‐exchanged zeolites, acting as reservoirs of silver species. The biocidal action of Ag‐Faujasite (Ag‐FAU) and Ag‐Linde Type A (Ag‐LTA) zeolites, containing different silver contents, is studied against different types of bacteria and fungi. Importantly, zeolite structure is found to be a significant parameter for controlling the antibacterial activity of Ag‐exchanged zeolites. The results show that Ag‐FAU presents a higher activity than Ag‐LTA, because the topology of FAU combined with its highest Si/Al ratio favors the formation and release of silver species with important biocidal activity. Some insights on the bactericidal mechanism of Ag‐zeolites are envisaged by means of high resolution transmission electron microscopy, showing the multi‐targeted biocidal action of Ag species released from zeolites. Besides, it is shown that Ag‐zeolites are more active against bacteria than fungi. Antifungal activity is highly dependent on the fungi species and the structure of the zeolite is not as determinant as it is for the antibacterial activity.

Removal of pathogenic bacteria from wastewater using silver nanoparticles synthesized by two fungal species

Nanotechnology are fast advancing and currently became more effective than the conventional technologies used in water treatment that offers safe opportunities for using unconventional water supply sources. Fungi are more versatile in growth and metal tolerance in contrast to bacterial population. This work aims to demonstrate the extracellular synthesis of silver nanoparticle by using two filamentous fungi Penciillium Citreonigum Dierck and Scopulaniopsos brumptii Salvanet-Duval isolated from Lake Burullus, examine the biosynthesized nano-silver particles by UV–vis spectroscopy, transmission electron microscopy (TEM). The functional group of protein molecules surrounding AgNPs was identified using Fourier transform infrared (FTIR) analysis. Check the antibacterial activity of biosynthesized silver nanoparticles at two concentrations (550.7 and 676.9 mg/l) and interact it with bacteria for different durations (15, 60 and 120 min). Polyurethane foam was used as silver carrier and nano-silver solution for the removal of pathogenic bacteria in polluted water. The synthesized AgNPs showed an excellent antibacterial property on gram positive and gram negative bacterial strains.

Mixed matrix membranes based on dual-functional MgO nanosheets for olefin/paraffin separation

Mixed matrix membranes (MMMs) comprising MgO nanosheets (MgO-NSs) and AgBF4 in a comb copolymer matrix were prepared for olefin/paraffin separation. The MgO-NSs with multi-mesopores and a large surface area were synthesized via a facile, non-hydrothermal method using MgCl2 as the precursor. Two kinds of comb copolymers, poly(oxyethylene methacrylate)-g-poly(ethylene glycol) behenyl ether methacrylate (POEM-g-PEGBEM) and poly(2-hydroxypropyl 2-(methacryloyloxy)ethyl phthalate)-g-poly(ethylene glycol) behenyl ether methacrylate (PHMEP-g-PEGBEM), were synthesized via low-cost, free-radical polymerization. The neat copolymer membranes showed poor separation efficiency (selectivity of 1.0), which was improved upon incorporation of AgBF4 via facilitated olefin transport. Addition of MgO-NS further enhanced the separation performance due to the dual-functionality, i.e., the enhanced activity of the silver carrier derived from its specific interaction with silver and increased diffusivity due to the mesoporous structure. The gas separation efficacy of the PHMEP-g-PEGBEM-based membranes was superior to that of the POEM-g-PEGBEM-based membranes, indicating the effectiveness of the PHMEP chain having the phthalate group for olefin separation due to strong chelation. The MMM consisting of PHMEP-g-PEGBEM/AgBF4/MgO-NS exhibited the optimal performance, (permeance of 11.8 GPU and selectivity of 12.9) for separation of the propylene/propane mixture. The specific interaction and morphological properties of the MMMs were characterized by various spectroscopic techniques.

Characterization, permeation analysis and stability increasing of facilitated transport membranes through incorporation of bis(bipyridine) silver (II) peroxydisulfate

Bis(bipyridine) silver (II) peroxydisulfate (Ag(bipy)2S2O8) has been applied as an alternative salt in the preparation of polyethersulfone (PES)/polyethylene oxide (PEO) facilitated transport membranes aiming at postponing the reduction process of silver carrier agents. The geometrical structure, mechanical and permeation properties of membranes containing Ag(bipy)2S2O8 or AgBF4 salts were compared in the ethylene/ethane separation process.Formation of silver nanoparticles from [Ag(bipy)2]2+ cations was lower than from Ag+, which was detected by means of UV–Visible spectroscopy and transmission electron microscopy (TEM). The two positive charges of [Ag(bipy)2]2+ cations besides oxidative properties of S2O82− anions postponed the reduction time of active sites. Ag(bipy)2S2O8 incorporated membranes possessed higher permeation, selectivity durability, mechanical strength and stronger CO bond strength and lower pore size and surface roughness than that of membranes containing AgBF4 salt. Lower lattice energy and steric hindrance of AgBF4 salt resulted in homogeneous distribution of Ag+ cations and counter-ions. The maximum selectivity of 124 was obtained at the highest AgBF4 concentration (molar percent=50%) and operational pressure (4barg). On the other hand, the maximum ethylene selectivity after saturation step belonged to the membrane containing (Ag(bipy)2S2O8) salt, which was 115 at the same condition.

Satellite TiO2 nanoparticles induced by silver ion in polymer electrolytes membrane for propylene/propane separation

Silver polymer electrolyte membranes containing inorganic nanoparticles have showed excellent facilitated olefin transport properties. However, the application of facilitated transport membranes has been significantly hampered because of the poor stability of silver ions carrier. The structural changes of the facilitated transport membranes corresponding to the reduced separation performance with an extended time have rarely been studied. In this study, titanium dioxide (TiO2) nanoparticles were introduced into poly(ethylene oxide) (PEO)/silver tetrafluoroborate polymer electrolyte membranes for propylene/propane separation. X-ray diffraction (XRD) analysis indicated that the addition of TiO2 and silver salt reduced the crystallinity of PEO. The selectivity of propylene/propane of the polymer electrolyte membrane increased with increasing concentration of silver salt and TiO2 in the polymer matrix. However, the propylene/propane selectivity decreased from 19.04 to 5.40 as the silver carrier ions became deactivated over the course of 196 h experiment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that the satellite TiO2 nanoparticles were formed around the silver salt after the composite membrane was placed in the air for 10 d. The findings in this work highlight the understanding of the carrier stability in polymer electrolyte membranes, and provide a potential opportunity to develop more stable polymer/carrier systems for the application of facilitated olefin transport membranes.

Silver salt facilitated transport membranes for olefin/paraffin separations: Carrier instability and a novel regeneration method

Facilitated transport membranes have been the subject of continuing study in the membrane gas separation field for over 50 years. Despite laboratory performance that far exceeds the polymer upper bound for many gas pairs, facilitated transport membranes have failed to achieve commercial success. This failure is in part due to instability of the carrier species that are responsible for the facilitation effect. Here, we describe the impact of exposure to light, hydrogen, hydrogen sulfide, and acetylene on a silver salt facilitated olefin transport membrane. All of these treatments are shown to significantly reduce the ethylene/ethane selectivity of membranes composed of a Pebax® 2533/AgBF4 selective layer. For example, the mixed-gas ethylene/ethane selectivity of such a membrane decreases from an initial value of 40 to 1.1 after 34 days of exposure to ambient light, due to photo-reduction of the silver carrier ions. In an effort to stabilize membrane performance, a regeneration method was discovered that uses a peroxide/acid liquid or vapor phase treatment to oxidize reduced silver carriers within the membrane. This in-situ regeneration method is shown to reverse the performance degradation of membranes exposed to light, hydrogen, and acetylene. Such a technique used in a cyclic process is a possible means of extending the lifetime of silver salt facilitated olefin transport membranes, and although many challenges remain, could play a role in moving these membranes toward practical reality.

A facile approach to a silver conductive ink with high performance for macroelectronics

An unusual kind of transparent and high-efficiency organic silver conductive ink (OSC ink) was synthesized with silver acetate as silver carrier, ethanolamine as additive, and different kinds of aldehyde-based materials as reduction agents and was characterized by using a thermogravimetric analyzer, X-ray diffraction, a scanning electron microscope, and a four-point probe. The results show that different reduction agents all have an important influence on the conductive properties of the ink through a series of complex chemical reactions, and especially when formic acid or dimethylformamide was used as the reduction agent and sintered at 120°C for 30 s, the resistivity can be lowered to 6 to 9 μΩ·cm. Furthermore, formula mechanism, conductive properties, temperature, and dynamic fatigue properties were investigated systematically, and the feasibility of the OSC ink was also verified through the preparation of an antenna pattern.

The effect of carrier salts blending on the morphology, stability and permeation properties of PES/PEO facilitated transport membranes

In this research, mixtures of Cu(NO3)2 and AgBF4 salts were used in preparation of poly(ethersulfone) (PES)/poly(ethylene oxide) (PEO) composite facilitated transport membranes. Reduction of carrier agent is known as the main challenge for this type of membranes. The effect of salt blending on the reduction behavior of silver carrier sites was analyzed through permeation and structural properties of composite membranes. Based on UV–Visible, mixed and ideal permeation experiments, the existence of copper divalent cations beside silver monovalent cations will result in delay in reduction time of silver cations. Therefore, the membrane selectivity is retained at higher values. However, starting selectivity of membranes containing silver salt ions (case 2) with concentration above threshold level is higher than other membranes containing both salts (case 1). TEM analysis proved that size and quantity of silver nanoparticles in the membranes of case 1 are less than membranes of case 2. Applying copper salt increased the potential of ions aggregated distribution in membranes structure according to FTIR–ATR analysis. Aggregation is one of the reasons for less initial separation potency in comparison with membranes without copper salt. Incorporation of cooper salt enhanced the surface roughness and mechanical strength of initial membranes containing silver salt alone.

ChemInform Abstract: Electrochemistry of Colloidal Silver Particles in Aqueous Solution: Deposition of Lead and Indium and Accompanying Optical Effects.

Colloidal silver particles (ca. 8 nm in diameter) act as microelectrodes in aqueous solution. They are charged via electron transfer from free radicals which are generated radiolytically. The stored electrons reduce adsorbed Pb2+ and In3+ ions. — The first monolayer of lead atoms deposited on the silver particles does not absorb at 215 nm where metallic lead has an absorption band. The Pb atoms cause the 380 nm surface plasmon band of the silver particles to be shifted to shorter wavelengths. This is explained in terms of electron donation from chemisorbed Pb atoms to the silver carrier. The Pb atoms of a submonolayer (which are formed by “under-potential” deposition) do not react with methyl viologen, MV2+, whereas the lead atoms deposited in subsequent layers (“Nernst potential” deposition) are readily oxidized by MV2+. The absorption spectrum of colloidal lead in water is also discussed (emax = 3.2 · 104 M−1 cm−1 at 215 nm). — Reduction of In3+ on the silver particles also leads to a blue-shift of the plasmon band. It is attributed to electron transfer from deposited In atoms. However, as In metal deposition proceeds, In+ is produced by the conproportionation of the indium metal with In3+. When almost all the In3+ ions have been reduced, indium metal is further deposited by In+ reduction. Silver particles carrying a tight indium shell absorb at 225 nm with e = 3.8 · 104 M−1 cm−1. This e-value is somewhat lower than the calculated one, and attributed to a reduction in mean free path for conduction electrons in small In colloids.

Effects of TiO 2 coating dosage and operational parameters on a TiO 2/Ag photocatalysis system for decolorizing Procion red MX-5B

In this study, titanium dioxide (TiO 2) powder was coated onto the surface of a dendritic silver (Ag) carrier to synthesize TiO 2/Ag for decolorizing Procion red MX-5B (MX-5B), and related operation factors were also studied. The results showed that even without ultraviolet-A (UVA) irradiation, the Ag carrier from the TiO 2/Ag catalyst had oxidizing ability, which could effectively degrade MX-5B color, but TiO 2 was ineffective. In addition, TiO 2 from TiO 2/Ag demonstrated photocatalysis performance when irradiated, and the Ag carrier further showed an electron-scavenging ability to mitigate electron–hole pair recombination, which can improve the photocatalytic efficacy. With the oxidization and electron-scavenging ability of Ag and the photocatalysis ability of TiO 2, TiO 2/Ag can decolor MX-5B more efficiently than TiO 2. The heavier Ag carrier also improves the solid–liquid separation of nano-TiO 2, making TiO 2/Ag more suitable for application in slurry systems of photocatalytic water treatment. When the TiO 2/Ag coating ratio was 50% by weight, there was a sufficient amount of TiO 2 on Ag's surface with a good distribution, and it exhibited a good photocatalysis decolorizing effect. In a study of how operational factors impact the decolorizing of MX-5B in the TiO 2/Ag photocatalysis system with UVA irradiation (UVA-TiO 2/Ag), the decolorization efficiency was optimal when the solution was maintained at pH 6.35. The addition of 0.01 M hydrogen peroxide (H 2O 2) aided the photocatalysis decolorization efficiency, although excessive H 2O 2 reacted with hydroxyl free radicals and decreased the active groups in the system, thereby reducing the photocatalysis activity. An operating temperature of 40 °C was conducive to MX-5B decolorization, which was better than operating at room temperature.

519 低温プラズマを用いた銀担体の生成とその殺菌効果(GS-2:一般セッション(2)材料)

519 低温プラズマを用いた銀担体の生成とその殺菌効果(GS-2:一般セッション(2)材料)

Silver-mediated separation of polyunsaturated fatty acids by oil-in-water emulsion liquid membranes.

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) ethyl esters were effectively separated from oleic acid (OA) and palmitic acid (PA) ethyl esters by oil-in-water (O/W) emulsion liquid membranes containing silver nitrates as a mobile carrier. Since the silver ions in the liquid membrane phase have a high affinity to the carbon-carbon double bonds in polyunsaturated fatty acids (PUFA), DHA and EPA ethyl esters were selectively transported through the complex formation with the silver carrier from the internal material phase to the external recovery phase. The stability of the liquid membranes in the O/W emulsions was the most important factor to achieve a high recovery yield of their PUFA esters with a high purity. Surfactants were limited to nonionic surfactants to obtain a stable emulsion liquid membrane when containing the silver carrier. Concentrations of the surfactant and silver nitrates had a predominant effect to operate the PUFA separation by emulsion liquid membranes effectively. There is an optimal concentration for the silver nitrates and excess dosage of the carrier causes the instability of liquid membranes. Under the best conditions, 86% polyunsaturated fatty acid esters were successfully separated through the silver liquid membrane in a few minutes with a 98% purity.

Electrochemistry of Colloidal Silver Particles in Aqueous Solution: Deposition of Lead and Indium and Accompanying Optical Effects

AbstractColloidal silver particles (ca. 8 nm in diameter) act as microelectrodes in aqueous solution. They are charged via electron transfer from free radicals which are generated radiolytically. The stored electrons reduce adsorbed Pb2+ and In3+ ions. — The first monolayer of lead atoms deposited on the silver particles does not absorb at 215 nm where metallic lead has an absorption band. The Pb atoms cause the 380 nm surface plasmon band of the silver particles to be shifted to shorter wavelengths. This is explained in terms of electron donation from chemisorbed Pb atoms to the silver carrier. The Pb atoms of a submonolayer (which are formed by “under‐potential” deposition) do not react with methyl viologen, MV2+, whereas the lead atoms deposited in subsequent layers (“Nernst potential” deposition) are readily oxidized by MV2+. The absorption spectrum of colloidal lead in water is also discussed (εmax = 3.2 · 104 M−1 cm−1 at 215 nm). — Reduction of In3+ on the silver particles also leads to a blue‐shift of the plasmon band. It is attributed to electron transfer from deposited In atoms. However, as In metal deposition proceeds, In+ is produced by the conproportionation of the indium metal with In3+. When almost all the In3+ ions have been reduced, indium metal is further deposited by In+ reduction. Silver particles carrying a tight indium shell absorb at 225 nm with ε = 3.8 · 104 M−1 cm−1. This ε‐value is somewhat lower than the calculated one, and attributed to a reduction in mean free path for conduction electrons in small In colloids.

Le dosage de traces d'argent dans le zinc extra-pur par activation neutronique

Below the p.p.m. level, the determination of silver in zinc by non-destructive γ-spectrometry is no longer feasible due to the activation of the matrix element. The activated zinc is dissolved in nitric acid, sulfamic acid and silver carrier are added, and 110mAg (253 d) is obtained in a radiochemically pure state after two successive electrolyses on gold cathodes.After two days of irradiation in a thermal neutron flux of the order of 3.1013 n/cm2/sec (BR2-Mol), 30 ng of silver can easily be evaluated with an error of 5%. Data obtained by integral γ-counting or by γ-spectrometry are compared.

A new principle of activation-analysis separations-IV: Substoichiometric determination of traces of silver

A substoichiometric determination of traces of silver in germanium dioxide and in metallic lead has been developed. It consists of simultaneous irradiation of a standard and test sample in a nuclear reactor followed by dissolution and addition of silver carrier. After adjusting the pH, the samples are extracted with the same substoichiometric amount of dithizone in carbon tetrachloride and the activities of the organic extracts measured. This single-step separation procedure is fully satisfactory because of its high selectivity. Moreover, substoichiometry avoids the necessity of determining the chemical yield. The procedure developed could be adapted without difficulty for the determination of traces of silver in other materials.