On the solubility of radium sulfate and carbonate
Radium is one of the most toxic elements and its concentration in different human activities and migration from man-made wastes provokes a strong interest in environmental science. To be able to model the migration process, reliable experimental thermodynamic data of radium compounds are needed.
In this work details of the safe radium source disassembly which were previously used in brachytherapy are described and different methods for conversion of RaSO4 into aqueous solution are reviewed. The method of choice included three cycles of RaSO4 heating in 1.5 M Na2CO3 up to 85 oC, cooling and subsequent removal of supernatant. X-ray diffraction studies showed that the method allows the synthesis of amorphous RaCO3, which can be dissolved in mineral acid. Gamma spectrometric measurements showed that most of the initial RaSO4 was converted into solution and that 7 ± 1 % of the initial 210Pb was co-precipitated with RaCO3. Synthesized RaCO3 was dissolved in HCl to prepare a radium stock solution. 
The radium stock solution was used to determine the solubility of pure RaSO4 and RaCO3 from oversaturation using Na2SO4 and Na2CO3 as a source of sulfate and carbonate ions. The solubility was determined at 25.1 oC as a function of ionic strength using NaCl media. The concentration of radium was measured by gamma spectrometry after separation of the aqueous phase from the solid phase using ultracentrifugation. The extended specific ion interaction theory was used to extrapolate solubility product constants to zero ionic strength (log10 Ksp° = -10.16 ± 0.05 for RaSO4 and log10 Ksp° = -7.73 ± 0.56 for RaCO3) and to calculate ion interaction coefficients.
A comparison of the shapes of the radium solubility curves for both anions with the shapes of corresponding barium solubility curves demonstrates the similarity of the behaviour of radium and barium salts in saline solutions. It can be supposed that due to the similarity of the radium and barium effective ionic radii, and the same charge, these ions undergo similar specific ion interactions in NaCl media.
Radium and Radioactivity
The radiations longest known to us are those capable of acting directly upon our senses; such are the rays of sound and light. But it has also long been recognized that, besides light itself, warm bodies emit rays in every respect analogous to luminous rays, though they do not possess the power of directly impressing our retina. Among such radiations, some, the infra-red, announce themselves to us by producing a measurable rise of temperature in the bodies which receive them, while others, the ultra-violet, act with specially great intensity upon photographic plates. We have here a first example of rays only indirectly accessible to us.
Limitations on the interpretation of biotite substitutions from chemical analyses of natural samples
Biotites, as well as other phases, are sufficiently complex chemically that there are numerous sets of linearly independent exchange components with which to describe the composition of a naturally occurring crystal. Even after complete chemical analysis, this leads to ambiguities in the correlation of exchange components with valid substitution mechanisms in complex phases. The best means of identifuing valid substitutions are by the observation of simple endmember compositions, the investigation of compositional changes in zoned crystals or petrogenetic sequences, and by direct experimental synthesis.