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純水在常溫下,介離度極小而此電阻極大。當含有電介質時,比電阻便相應降低。所以可用水的比電阻來表示其雜質之含量。表1是比較幾種不同處理方法所得水之純度。 要得到接近絕對純度的水非常困難,因為水的溶解能力很强;從空氣中、流經的管道、容器壁等處都容易溶入雜質。Kohlrausch与Heydweillert曾用石英器皿低溫減壓重覆蒸餾42次,在極小心的操作下,得到極少量比電阻为23.3 MΩcm~(-1)的純水。
Pure water at room temperature, low dielectric anisotropy and this resistance is extremely large. When the dielectric contains, the specific resistance is reduced accordingly. Therefore, the specific resistance of water can be used to indicate the content of impurities. Table 1 compares the purity of water obtained from several different treatments. It is very difficult to obtain water of near absolute purity because of its strong ability to dissolve the water; it is easy to dissolve impurities from the air, through pipes, container walls and the like. Kohlrausch and Heydweillert once distilled 40 times under low temperature and pressure in a quartz vessel to obtain pure water with a very small specific resistance of 23.3 MΩcm -1 under the careful operation.