This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
This is also an excellent clarifying medium, and can be used with the same advantage and in all cases where silica is intended to be used for plain or acidified syrups likewise, as it is also indifferent to the action of fruit-acids. It is lighter than sand and of greater fineness in powder, and therefore in finer division in the syrup. It clarifies also by subsidence but more slowly, yet thoroughly, and is in many cases preferred to sand. Natural pumice stone is found m the neighborhood of volcanoes, and used in solid form for polishing purposes and as a polishing powder. It consists of a combination of silica, alumina, calcium, magnesia, iron, alkalies, etc. Its artificial production has grown to be a special industry, and it is produced in so high a state of purity, that we must recommend the artificial product instead of the natural one.