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<br />'~1l-' <br /> <br />. in the float-in methods of canal 'sealing. However, a promising way <br />of overcoming this problem is being investigated. <br /> <br />Swelling~ -. This test measures the amount of swelling <br />that a akes place when a clay sample is dropped into water. A slight <br />amount of swelling is helpful because of its healing or hole-closing effect <br />on newly. placed clay layers when wetted for the first time. A large <br />amount of swelling, however, can introduce troublesome problems-- <br />especially in areas where the irrigation waters are hard and where severe <br />frost and drying occur during the winter time. <br /> <br />Other tests -- In addition to the characteristics that can be <br />determined in the test procedures already described, several other <br />characteristics of clay are important from a canal and pond sealing <br />standpoint. ciays are commonly referred to as inert materials formed <br />by the chemical decomposition of rock materials. The decomposition <br />part is true in a general sense, but many clays are far from inert. They <br />have certain chemical characteristics that profoundly affect theil' aeoUing <br />characteristics. For example, a so-called ''black-alkali'' soil can in some <br />instances be changed from a gummy tight unmanageable soil to a loose <br />crumbly open soil by the application of gypsum. This, of course, is to <br />be avoided in canal and pon9- sealing work. Thus, it is important, <br />especially from a service or sealing endurance standpoint, that the major <br />chemical and mineralogical traits of a sealing clay are known. Detailed <br />evaluations of this type are planned for samples from those deposits now <br />being commercially developed. <br /> <br />1033 <br />