US PATENT SUBCLASS 423 / 340
.~.~.~ By purifying sand

Current as of: June, 1999
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423 /   HD   CHEMISTRY OF INORGANIC COMPOUNDS

324  DF  SILICON OR COMPOUND THEREOF {4}
325  DF  .~ Oxygen containing {2}
335  DF  .~.~ Silica {5}
340.~.~.~ By purifying sand

DEFINITION

Classification: 423/340

(under subclass 335) Processes which include the step of purifying silicon dioxide.