Heterogeneous exchange of precipitates

Summary The heterogeneous exchange of ferric ion between a labelled aqueous ferric chloride solution and some differently prepared ferric (hydr)oxides [(1) a freshly formed “amorphous” ferric (hydr)oxide, (2) ferric oxide obtained by drying the freshly formed precipitate in the air at 165 °C for 4.5 hours, (3) ferric oxide obtained by boiling the freshly formed precipitate in water at 100 °C for 4.5 hours] was investigated at room temperature. The exchange rate decreased in the sequence: (1), (2), (3), that sequence being attributed to the recrystallization of the solid phase in the sense of lattice ordering and particle growth, related to the treatment of freshly formed precipitate before the solid was put in contact with the ferric chloride and labelled. System (1) corresponded to a positively charged precipitate near the equivalency of the system FeCl₃ + NaOH, and the exchange was governed by a rapid recrystallization (particle growth), initiated by labelling⁵⁹FeCl₃ solution in an acid (HCl) medium. In the system (2) selfdiffusion is indicated as the exchange governing process. The radionuclide⁵⁴Mn, being present without isotopic carrier in labelling⁵⁹FeCl³ solution and introduced into the liquid phase, remained in the liquid phase of systems (2) and (3). Contribution number 112 from the Department of Physical Chemistry, Faculty of Sciences, University of Zagreb.     

Intense Dyes through Chromophore–Chromophore Interactions: Bi- and Trichromophoric Perylene-3,4:9,10-bis(dicarboximide)s

Simple perylene dyes , which are known for their high extinction coefficients, are converted into intense and highly fluorescent (at ca. 540 nm) dyes such as 1 by a directed chromophore–chromophore coupling. Molar extinction coefficients of more than 400 000 L mol⁻¹ cm⁻¹ are attained. R = CH(C₆H₁₃)₂, CH(C₇H₁₅)₂, CH(C₉H₁₉)₂.     

Evidence for 2 × 1 building block in the atomic structure of Si{111} 7 × 7

The well known experimental Si {111} 7 × 7 LEED pattern is shown to exhibit systematic enhancement of diffracted intensity at the $\text{1}\text{2}$-order positions, thus revealing the existence of 2 × 1 or 2 × 2 structural components in the 7 × 7 structure with a single domain Si {111} 2 × 1 cleaved structure reveals remarkable similarities. The conclusion is that the fundamental building block of the 7 × 7 structure is a 2 × 1 subunit which closely resembles the unit cell of the cleaved 2 × 1 structure.     

Discrete charges and condenser double layer models in colloid chemistry

Summary The conclusion is drawn from results on the constituent and counter ion adsorption on silver iodide and bromide from different laboratories that the double layer model of colloidal particles, given as the arithmetical sum of a finite number of discrete ion charges, can be considered as a more probable correct approximation instead of that given by the homogeneous flat plate or sphere condenser model. Published experimental confirmations of the concept of discrete charges in the theories of colloid stability and coagulation, of counter ion adsorption and of electrokinetics are listed.

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Zusammenfassung Es werden Resultate über die Ionen- und Gegenionenadsorption an Silberjodid und Bromid zitiert, von welchen die Schlu?folgerung gezogen wird, da? an kolloidalen Prim?rteilchen das Doppelschichtmodell, das als die arithmetische Summe einer endlichen Zahl von diskreten Ionenladungen gegeben ist, als eine wahrscheinlichere Approximation angenommen werden kann als das Modell, das durch den homogenen Platten- oder Kugelkondensator dargestellt ist. Publizierte experimentelle Best?tigungen des Konzepts der diskreten Ionenladungen in den Theorien der Stabilit?t und Koagulation der Kolloide, der Gegenionenadsorption und der elektrokinetischen Erscheinungen werden zitiert.