ASCORBIC ACID as an analytica Sveh1a.l MildThe kinetics of reduction of silver([) have been studied in perchloric acid solution using ascorbic acid (AH,) as the reducing agent. First-order dependences on ascorbic acid and silver(i) concentrations are exhibited, together with an inverse first-order dependence on [H+]. The influence of ionic strength (1 < 0 . 0 8 ~) is negligible. The activation energy is 10.6 A 0.2 kcal mot-l. A mechanism for the reduction process is proposed which invoives bimolecular rate-determining reaction between ascorbate ion and silver(1).
Kinetics of the osmium(v1il) -catalysed oxidation of glycollic, lactic, and mandelic acids have been investigated in alkaline media. First-order rate plots in chloramine-Twere linear up to two half-lives. However, under pseudofirst-order conditions the rate constants showed a slight decrease with increase in chloramine-T concentration. The rate of reaction was independent of a-hydroxy-acid concentration and directly proportional to the osmium-(VIII) and the reciprocal of the hydroxide ion concentrations. The formation of a complex between N-chlorotoluene-p-sulphonamide and osmium(V1li) is rate-determining and is followed by the rapid transfer of a hydride ion from the substrate to this complex.
Although cercarial dermatitis is an emerging disease world-wide, cases of such dermatitis may often go undiagnosed, especially in communities that are affected by various skin infections. Between August 2001 and July 2002, 1336 individuals from tribal villages in central India were examined for dermatitis. Skin scrapings were collected and examined for Sarcoptes scabiei and each subject's response to antiscabies treatment was recorded. Freshwater snails were collected from the local ponds used for bathing, and examined for cercariae. The recorded prevalence of dermatitis ranged between 2.1% and 12.5% during the study year, peaking at the end of winter (February-March) and during the rainy season (August-October). Snail positivity for cercariae peaked in the rainy season. The prevalence and the severity of dermatitis were both higher in children than in adults. As most recorded cases of dermatitis were associated with a rash that developed soon after bathing in the local pond, all the skin scrapings were negative for itch mites, and the response to antiscabies treatment was poor, most if not all of the dermatitis observed was probably cercarial. Cercarial dermatitis therefore appears to be a significant health problem among the tribal populations of central India.
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