Liesegang rings of copper chromate in gelatin gel

Summary DistinctLiesegang Rings of Copper chromate in gelatin gel are not formed as the salt forms a very stable colloid in this medium. As this sol is coagulated by KH₂PO₄, well defined rings of Copper chromate in gelatin gel are formed in the presence of this electrolyte.

---

Zusammenfassung DeutlicheLiesegang-Ringe werden in Kupfer-Chromat und Gelatine-Gel nicht gebildet, da das Salz ein sehr stabiles Kolloid in diesem Medium darstellt. Wenn dieses Sol durch KH₂PO₄ koaguliert wird, entstehen definierte Ringe von Kupfer-Chromat im Gelatine-Gel bei Gegenwart dieses Elektrolyten.

     

Liesegang rings of lead iodide Part II

DistinctLiesegang rings of lead iodide in gelatin gel are not formed as the salt forms a very stabilised colloid in gelatin medium. The stability of the colloid has been investigated. This sol is precipitated by potassium iodide and barium nitrate. Well definedLiesegang rings of lead iodide are formed in the gelatin gel in the presence of electrolytic barium nitrate.     

Formation of Liesegang rings of mercuric chromate and the effect of gel medium on the condition of mercuric chromate

Summary For the formation of well defined Liesegang rings in different gel media, it is essential to study the effect of gel medium on the condition of the insoluble salt. In case of mercuric chromate, the well defined rings were developed in agar agar and starch gel as the sol formed is coagulable by one of the reactants. In gelatin medium, a very stable sol of mercuric chromate is formed, which is coagulated by hydrochloric acid. Beautiful bands of mercuric chromate were formed in gelatin gel only in presence of hydrochloric acid.

---

Zusammenfassung Zur Bildung von gut definierten Liesegang-Ringen in verschiedenen Gel-Medien ist es wesentlich, die Wirkung des Gel-Mediums auf die Bedingung des unl?slichen Salzes zu untersuchen. Im Fall von Quecksilber werden die gut definierten Ringe in Agar-Agar und St?rkegel entwickelt, wenn das gebildete Sol durch einen der beiden Reaktanten koaguliert werden kann. In Gelatine wird ein sehr stabiles Sol von Quecksilber-Chromat gebildet, welches durch Salzs?ure koaguliert wird. Sehr sch?ne Ringe von Quecksilbersulfat bilden sich in Gelatinegel nur in Anwesenheit von Salzs?ure.

     

Effect of the rate of diffusion of ions on the periodic precipitation of silver chromate

The effect of the rate of diffusion on the formation ofLiesegang rings of silver chromate in gelatin and agar agar medium has been studied. The rate of diffusion of silver ions in the agar agar gel is much slower than that in gelatin gel during the formation of rings of silver chromate. If the rate of diffusion of silver ions in agar agar gel is increased, even then rings do not form. The only change brought about by the rate of diffusion is for the distance between the successive rings.

---

Zusammenfassung Der Einflu\ der Diffusionsgeschwindigkeit auf die Bildung vonLiesegang-Ringen aus Silberchromat in Gelatine und Agar-Agar wurde untersucht. Die Diffusionsgeschwindigkeit der Silberionen in den Agar-Agar-Gelen ist viel niedriger als in den Gelatinegelen während der Bildung der Ringe von Silberchromat. Wenn die Diffusionsgeschwindigkeit der Silberionen in Agar-Agar-Gelen gesteigert wird, bilden sich schlie\lich überhaupt keine Ringe. Der einzige Einflu\, den die Diffusionsgeschwindigkeit hervorruft, ist also änderung des Abstandes aufeinanderfolgender Ringe.

     

Condition of silver chromate in different media

The condition of silver chromate in aqueous, gelatin, agar agar, and starch sols has been studied. It has been found that in the gelatin medium, more of silver chromate is present in ionic state due to the acidity of the medium. The condition of the insoluble substance in agar agar and starch sol is similar to that in the aqueous medium.

---

Zusammenfassung Der Zustand des Silberchromates in wä\rigen Gelatine-, Agar-Agar- und Stärkesolen wurde untersucht. In Gelatine ist mehr Silberchromat im Ionenzustand vorhanden, wegen der Azidität des Mediums. Der Zustand der unlöslichen Substanz in Agar-Agar- und Stärkesol ist ähnlich wie der in Wasser.

     

Phasenumwandlung zweiter Art bei der Gelbildung

During theLiesegang ring formation of lead chromate in an agar agar gel it was observed that broad bands are formed in the presence of light whereas finer bands are obtained in dark. This difference in behaviour is due to the fact that lead chromate forms a more stable sol in light as compared to that in the dark.     

Liesegang rings of lead chromate Part II

Faint rings of lead chromate are formed in gelatin gel when a solution of lead nitrate diffuses in gelatin gel containing potassium chromate. These rings become well defined in the presence of a coagulant like potassium nitrate. Well definedLiesegang rings of insoluble substances in gel media can be obtained if the substance can exist in the colloidal state in the media and is coagulable by the diffusing ion.     

Ionic Dependence of Gelatin Hydrogel Architecture Explored Using Small and Very Small Angle Neutron Scattering Technique

The hierarchical structure of gelatin hydrogels mimics a natural extracellular matrix and provides an optimized microenvironment for the growth of 3D structured tissue analogs. In the presence of metal ions, gelatin hydrogels exhibit various mechanical properties that are correlated with the molecular interactions and the hierarchical structure. The structure and structural response of gelatin hydrogels to variation of gelatin concentration, pH, or addition of metal ions are explored by small and very small angle neutron scattering over broad length scales. The measurements of the hydrogels reveal the existence of a two‐level structure of colloid‐like large clusters and a 3D cage‐like gel network. In the presence of Fe³⁺ ions the hydrogels show a highly dense and stiff network, while Ca²⁺ ions have an opposite effect. The results provide important structural insight for improvement of the design of gelatin based hydrogels and are therefore suitable for various applications.     

Buchbesprechungen

The effect of the solubility of insoluble lead chromate in the formation ofLiesegang rings has been studied. Rings are less closely packed as the solubility of lead chromate is increased with the increasing acidity of the medium. For the same concentration of potassium dichromate diffusing in the agar agar gels containing solutions of lead nitrate, it is observed that rings become more close as lead nitrate solution is diluted, a fact which is usually not observed in theLiesegang ring formation of different substances.     

Conditions of the formation of yellow sol of silver chromate

Yellow sol of silver chromate is obtained in gelatin medium when the reactants are either dilute or when the amount of silver nitrate is lesser than the equivalent amounts. In agar agar and aqueous medium, yellow sol is obtained in the presence of sodium citrate. This yellow sol is suddenly converted into a red suspension after a certain period. The time of conversion of yellow sol to red suspension increases as the reactants are diluted or concentration of sodium citrate is increased or when the amount of silver nitrate added is reduced. In presence of sodium citrate and smaller concentrations of AgNO₃, a stable yellow sol could be obtained in aqueous medium.

---

Zusammenfassung Gelbes Silberchromatsol wird in Gelatine erhalten, wenn die reagierenden Komponenten entweder verdünnt sind oder wenn der Betrag an Silbernitrat geringer als äquimolekular ist. In Agar-Agar und Wasser wird gelbes Sol in Gegenwart von Natriumzitrat erhalten. Dieses gelbe Sol wandelt sich plötzlich nach einer gewissen Zeit in eine rote Suspension um. Diese Zeit wächst, wenn die Reagenzien sehr verdünnt sind oder die Konzentration des Natriumzitrats gesteigert wird oder der Anteil an zugefügtem Silbernitrat verringert wird. In Gegenwart von Natriumzitrat und kleinen Konzentrationen von Silbernitrat konnte in Wasser ein stabiles gelbes Sol erhalten werden.

     

Precipitation of barium chromate in the presence of strontium and lead by complexation followed by volatilization of ammonia

Cation-release is used to precipitate barium chromate from homogeneous solution in the presence of lead and strontium. MEDTA or DCTA is added to complex the metal ions at pH 10.3 (adjusted with ammonia). On heating, the ammonia slowly volatilizes and the consequent increases in acidity releases the metal ion bound in the least stable chelate (barium). Precipitation is about 99.3-99.7% complete at pH 6.7-6.8, with less than 0.1% co-precipitation of lead or strontium. Lower pH values can be attained by volatilizing acetic or hydrochloric acid into the solution in a closed system.     

Nephelometric determination of gold with di-2-thienyl-ketoxime

A nephelometric method for the determination of microgram quantities of gold with di-2-thienylketoxime is described. The yellow gold complex, which has the empirical formula Au(C₉H₆NOS₂)₂OH, forms a stable suspension when gelatin is added as protective colloid. Many foreign ions do not interfere in 5-fold amounts. If necessary, a preliminary isopropyl ether extraction of gold can be used.     

超细颗粒卤化银的制备与稳定性

卤化银微晶体是一种典型的与成像材料相关的无机微粒子。一个多世纪以来,它所特有的光敏性能使之在成像科学领域中一直占据着重要的地位。近二十年来,纳米粒子化学和物理的迅速发展对于推动成像科学技术前进产生了不可低估的影响。纳米级超细颗粒卤化银的制备与性能研究十分活跃,它不仅对于深入认识卤化银成像机理具有重要意义,而且在形成新的特殊照相材料如超高解像力照相材料等方面起着关键性作用。超细颗粒卤化银的制备方法基本上可概括为两种,即直接反应法与间接反应法。前者是在某种保护性介质中同时注入银盐与卤盐,使之直接反应…     

Precipitation of barium chromate from homogeneous solution using complexation and replacement A separation of barium from relatively large amounts of strontium and lead

A new procedure is presented that efficiently separates barium from relatively large amounts of strontium and lead. The barium is precipitated as the chromate from a solution in which the multivalent cations are complexed with EDTA. The barium ions are homogeneously released in solution when magnesium ions are slowly introduced into the solution. The magnesium ions gradually replace the barium ions from their EDTA complexes, bringing about a precipitation of barium chromate from homogeneous solution.

This slow formation of barium chromate crystals holds co-precipitation to a minimum and produces crystals that are easily filtered and washed. More than 99.7% of the barium can be precipitated as the chromate, with less than 0.6% of the strontium, when the two ions are in equal molar concentration.     

Indirect radiotracer study of the adsorption of chromate ions on γ-Al2O3 and direct study of the adsorption of sulfate ions on Cr2O3 using 35S-labelled H2SO4

The specific adsorption of sulfate ions on Cr₂O₃ was studied by a radiotracer technique using ³⁵S-labelled sulfuric acid in low concentrations (c<10^–3 mol dm^–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined. It was found that the extent of adsorption is determined by the protonation of the surface sites, similar to other oxides studied previously. A comparison of Cr₂O₃ and Al₂O₃ in this respect shows that the protonation of the former takes place at significantly lower pH values than that of the latter. The indirect radiotracer study of the adsorption of chromate on Al₂O₃ was carried out using labelled sulfate ions as indicator species. The results obtained show that the adsorption strength of chromate species is very low in comparison to sulfate ions and a regular Langmuir-like adsorption behaviour can be observed. It is believed that the observations presented may contribute to a better understanding of the behaviour of surface layers with a mixed oxide content. Electronic Publication     

Determination of traces of mercury and barium in mineral-containing water by selective retention on ion-exchange papers and x-ray fluorescence spectrometry

Mercury(II) is collected from dilute hydrochloric acid solutions on anion-exchange paper disks; barium ions are collected on cation-exchange paper disks after separation by coprecipitation with lead chromate and dissolution of the precipitate in 1,2-diaminocyclohexanetetraacetic acid which also serves as masking agent. The disks are then subjected to x-ray fluorescence spectrometry. The method is satisfactory for mg kg^?1 levels of the two ions in the presence of large amounts of sodium, calcium and magnesium ions (e.g., in synthetic sea water and Contrexeville water). Various procedural modifications are discussed.     

Liesegang rings — Part I

Summary The conditions for the formation of revert type ofLiesegang rings have been studied here. Various systems of rhythmic precipitations of silver chromate are produced in a mixtures of agar and gelatin gels under different environmental conditions. Ring systems of silver, copper and other ferricyanides have also been studied in gelatin gel. The observations show that the cause of the revert systems ofLiesegang rings is the high peptizability of the precipitating matter in the media containing gel and the unreacted ions.

---

Zusammenfassung Die Bedingungen der Bildung des „umgekehrten“ Types vonLiesegang-Ringen wurden untersucht. Verschiedene Systeme rhythmischer F?llung von Silberchromat wurden in einer Mischung von Agar und Gelatinegelen unter verschiedenen Umgebungsbedingungen erzeugt. Ringsysteme von Kupfer, Silber und anderen Ferricyaniden in Gelatine wurden untersucht. Die Beobachtungen zeigen, da? die Ursache für die „umgekehrten“Liesegang-Ringe in der hohen Peptisierbarkeit der Füllsubstanz im gelhaltigen Medium und den noch nicht reagierten Ionen liegt.

     

Nucleation of lead chromate from homogeneous solution

On the basis of the Christiansen-Nielsen model for nucleation, the nucleus of lead chromate precipitated from homogeneous solution has been found to consist of about five ions. The critical supersaturation values of solutions of lead chromate are dependent upon the method of filtration; however, a change in supersaturation of about 25 % is without effect on the size of the critical nucleus.     

Complex citrates of metals in inorganic analysis

Summary A new method has been described for the quantitative separation of silver and lead in a solution. The method consists of adding an excess of sodium citrate solution to the solution of the mixture, when the insoluble citrates of silver and lead which at first precipitate out, redis-solve due to the formation of complex citrates. By the addition of hydro-chlorid acid to the solution, only silver chloride precipitates out and may be estimated gravimetrically. In the filtrate lead may be estimated gravimetrically as lead chromate. The method described here is quite reliable, as the results obtained by the analysis of a number of mixtures of different compositions have been found to be very satisfactory, the errors lying within permissible limits.     

Chloride-catalyzed oxidation of phenol in pulsed-laser irradiation titanium dioxide sols

The kinetics of photolysis of phenol in presence of two kinds of TiO₂ colloid in acid aqueous solution medium was studied by transient absorption spectroscopy. The absorbance and quantum yield of the phenoxyl radicals is strongly influenced by the chloride ions. The process of laser flash photolysis of phenol in the presence of chloride has been discussed.