At the same time Berzelius obtained the element, in an impure condition, by fusing silica with charcoal and iron in a blast furnace; its preparation in a pure condition he first accomplished in 1823, when he invented the method of heating double potassium fluorides with metallic potassium. [Please select]
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Of course only neutral fluorides are available for use in soap, acid fluorides and soap being obviously incompatible. [Please select]
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