The adsorption of water vapor on the surface of glass has been extensively studied. As early as 1830, Faraday (11) pointed out the large adsorptive capac-

Natural Organic Matter (NOM) is found in all surface waters. An increase in the amount of NOM over the past 10-20 years has been observed in raw water supply in many areas in Egypt, which has had a significant impact on drinking water treatment. Water scarcity and the increased contamination of drinking water has led to increased doses of coagulants and disinfectants used in water treatment, which has led to increased sludge volume and the production of harmful residual byproducts. In this paper, the results of experiments using an experimental model carried out to investigate improving the removal efficacy of NOM using a natural coagulant, such as chitosan, along with alum, are presented. The results show the use of chitosan is effective in removing NOM and reducing algae and turbidity. In addition, a dose of chitosan added to alum successfully reduced the amount of alum needed in the purification process.

been reported to proceed rather faster than with the thoriurri tartrate. The alteration of the tartrate rotation in response to this direct attack on one of the centers of optical activity needs no comment. The quantitative relation with alkalinity suggests a quantitative correlation with completeness of the transformation to the ionized form or forms.Darmois and Heng3 presented evidence for a 1: 1 complex of tartrate and thorium in relatively acid solutions, but the lack of pH control greatly diminishes the significance of this evidence. Their data also show there must be another complex, probably with two tartrates per thorium, but again little more could be said. Bobtelsky (7) E.g , S.and Grauss have also published a paper on thoriumtartrate complexes, which is based on "heterometric" (nephelometric) titrations. We can say little about this work other than that the authors did not seem to be aware that thorium tends to hydrolyze in all but reasonably acid solutions, and proceeded to mix solutions of very different pH values to obtain their results. Further, we do not see horn the authors could have obtained the quantitative results reported, in view of the qualitative behavior we observed on adding thorium solutions to tartaric acid solutions and vice versa. At the least, their results must be highly dependent on the exact details of solution concentration, etc. , and the interpretation correspondingly uncertain. (8) M. Bobtelsky and B. Gratis, Bull. Res. Council Israel, 3, 83Sorption isotherms of water vapor on completely and partially dehydrated native and precipitated gypsum are similar. Quick uptake is noted a t very low vapor pressures followed by an almost horizontal plateau in the isotherm until saturation pressure, when the uptake becomes a function of time. Sorption-desorption along the plateau is reversible, but hysteresis becomes pronounced when desorption is carried out from sorption values a t saturation. The isotherm is then parallel to the sorption plateau but displaced to higher values depending on the time of exposure to saturation pressure. When dehydration of gypsum is conducted below 400°, the initial quick uptake of water corresponds to the formation of the hemihydrate. The dihydrate is formed after several days' exposure of the hemihydrate to saturated water vapor. But exposure for several days to water vapor a t a pressure 3.5% short of saturation results in an uptake only slightly greater than corresponds to the formation of the hemihydrate, although raising the pressure to the saturation value induces further uptake to an amount exceeding that required to form the dihydrate. Dehydration above 500' renders the anhydrite incapable of forming the dihydrate] although the hemihydrate may still be formed. Sorption isotherms on partially dehydrated gypsum show a linear relation between the amount of formed hemihydrate and the percentage of decomposition when dehydration is a t 150".It is concluded that the transformation of the anhydrite into the hemihydrate in presence of water vapor is a qu...