Excess molar volumes and excess partial molar volumes of diethylene glycol monoethyl ether - <i style="mso-bidi-font-style:normal">n</i>-alcohol mixtures at 298.15 K

237-243Excess molar volumes VmE have been measured for binary mixtures of diethylene glycol monoethyl ether with methanol, ethanol, 1- propanol, 1-pentanol and 1-hexanol as a  function of composition using a continuous-dilution dilatometer at 298.15 K. The excess molar volumes VmE are negative over the entire range of composition for the systems diethylene glycol monoethyl ether + methanol, + ethanol ,  and + 1-propanol and positive for the remaining systems, diethylene glycol monoethyl ether + 1-pentanol, and + 1-hexanol. The measured VmE values increase towards positive direction with increase in chain length of the n-alcohol. The VmE results have been used to estimate the excess partial molar volumes VmE .i of the components and have also been analysed using the Prigogine - Flory – Patterson (PFP) theory. An analysis of each of the three con<span style="font-family:HiddenHorzOCR; mso-bidi-font-family:HiddenHorzOCR">tributions viz. interactional, free volume and internal pressure to VmE shows that the free volume effect and internal pressure contribution are negative for all the mixtures, whereas the interactional contribution is negative for methanol and positive for remaining systems. The behaviour of VmE , VmE .i and 12 (Flory's interaction parameter) with composition and the number of carbon atoms in the alcohol molecule is discussed.   <span style="font-family:HiddenHorzOCR; mso-bidi-font-family:HiddenHorzOCR"><span style="font-family:HiddenHorzOCR; mso-bidi-font-family:HiddenHorzOCR"><span style="font-family:HiddenHorzOCR; mso-bidi-font-family:HiddenHorzOCR"></span

Fluoride Contamination in Drinking Water -A Review

Abstract Drin king water is the largest contributor of fluoride in daily intake. Dissolution of fluoride-containing rock minerals is the source of naturally occurring fluorides in groundwater whereas application of phosphate fertilizers or sewage sludges or pesticides are the artificial source of fluoride in groundwater and surface water. Fluoride concentrations beyond the standards cause dental and skeletal fluorosis. Fluoride to xicity can also cause non-skeletal diseases like aches and pain in the joints, non-ulcer dyspepsia, Po lyurea (tendency to urinate more frequently) and polydipsia (excessive thrust), muscle weakness, fatigue, anemia with very low hemoglobin levels, etc besides other reasons. Many researchers have used various types of inexpensive and effective adsorption mediu m like clays, solid industrial wastes such as red mud, spent bleaching earths, spent catalysts and fly ash, activated alu mina, carbonaceous materials, bone charcoal, natural and synthetic zeolites, etc. for the treatment of fluoride contamination. Th is paper presents a rev iew, which focuses on the sources of fluoride in drinking water, its impacts on health and different control measures