Answer: D. Soluble matters
Smith test is used for determining soluble matters.
Smith test is performed to determine presence of soluble matter in stone samples. In this test first of all take some samples of stone, and they are placed in a glass tube.
Now the tube is filled with water. After one hour the tube is strongly shaken. Clear water is converted into dirty water by the presence of earthy matters. It indicates the presence of soluble matters in stone. Hence, Smith test is used for determining soluble matters.
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