flint: a hard kind of stone; a form of silica more opaque than chalcedony
silica: a white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earth's crust as quartz or cristobalite or tridymite or lechatelierite
fehling's solution: a liquid solution of copper sulfate and potassium tartrate and sodium hydroxide that is used to test for sugar in the urine; solution turns reddish when sugar is present