Experimental materials and

At this stage one of the most urgent tasks is a re-investigation of a wide range of systems by other than kinetic methods, especially by spectroscopy and conductivity measurements. It may be useful to point out here that, if more investigators had taken an old-fashioned natural historian s view of their experimental material and had noted and recorded the presence or absence of colours in reacting systems, and followed up these clues, the present situation might never have arisen. 

Evershed RP, Bethell PH, Reynolds PJ, Welch NJ, 5P-Stigmastanol and related 5 3-stanols as bio markers of manuring Analysis of modern experimental material and assessment of the archaeological potenxi A, J Archaeological Science 24 485-495, 1997. 

Plasma chemistry is at present mainly an empirical technique. Little is known about relationships between the properties of the plasma and the reaction mechanism or the product distribution. Experimental conditions have to be optimized for every new reaction. Once more experimental material and improved methods of diagnosing plasma become available it may become routine to adjust plasmas for each specific chemical problem. 

Sampling and Measurements. The determination of dissolved actinide concentration was started a week after the preparation of solutions and continued periodically for several months until the solubility equilibrium in each solution was attained. Some solutions, in which the solubilities of americium or plutonium were relatively high, were spectrophotometrically analyzed to ascertain the chemical state of dissolved species. For each sample, 0.2 to 1.0 mL of solution was filtered with a Millex-22 syringe filter (0.22 pm pore size) and the actinide concentration determined in a liquid scintillation counter. After filtration with a Millex-22, randomly chosen sample solutions were further filtered with various ultrafilters of different pore sizes in order to determine if different types of filtration would affect the measured concentration. The chemical stability of dissolved species was examined with respect to sorption on surfaces of experimental vials and of filters. The experiment was performed as follows the solution filtered by a Millex-22 was put into a polyethylene vial, stored one day, filtered with a new filter of the same pore size and put into another polyethylene vial. This procedure was repeated twice with two new polyethylene vials and the activities of filtrates were compared. The ultrafiltration was carried out by centrifugation with an appropriate filter holder. The results show that the dissolved species in solution after filtration with Millex-22 (0.22 ym) do not sorb on surfaces of experimental materials and that the actinide concentration is not appreciably changed with decreasing pore size of ultrafilters. The pore size of a filter is estimated from its given Dalton number on the basis of a hardsphere model used in the previous work (20). 

The number of possibilities thus may be bewilderingly large, and it may seem to be a hopeless task to find the correct mechanism. However the experiments will always show the investigator certain pecularities of the reaction which exclude a number of assumptions. Other assumptions may be so improbable from a chemical point of view that they also can be excluded. In short, a chemist who has provided the experimental material and who has some experience in kinetics will have a good chance of finding the right mechanism, i.e., the mechanism from which his experimental results can be derived. 

---