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 a good filter-medium for clarifying syrups. Common sand will not answer, as it contains too much lime and other impurities (organic matters, etc.) It must be pure silica (quartz) or glass-sand, or it will do more harm than good, and this can be had in chemical purity and at a low price at any bottlers' supply house. Its use is unlimited; it is the filter-medium for all kinds of syrups, acidulated or not, as it is indifferent to the action of fruit-acids, and it is very effective. By its gravity it acts as a clarifier, precipitating impurities. It is best sifted or sprinkled over the syrups. Against its use, it is said, that it sinks too rapidly and therefore appears to be less useful. This we consider wrong. If of proper fineness and used in sufficient quantity it will precipitate all suspended impurities. A good way is to agitate it thoroughly with the syrup. Then let subside, which it will do rather quickly and thereby clarify quite perfectly. Subsequent filtration will turn out a fine product. If time permits and extra precaution is desired, agitate the sand and syrup well and pour the mixture into the filtering bag in order to allow some sand to accumulate on the filter. This method will clarify the syrup to perfection, but necessarily slow. If too much sand accumulates, filtration will stop altogether. Therefore, where this additional precaution is applied, it is advisable to run only the first portions of the agitated syrup (thoroughly mixed with the sand) through the filter, and let the balance subside and clarify in the syrup-vessel, and afterwards filter the remaining syrup through the slight layers of sand which the first portion has left on the filter, which will then clarify and filter out even the last trace of suspended impurities. But it will in most cases be sufficient to agitate the syrup with the sand and allow the latter to subside previous to filtration.
Asbestos, powdered, used for the filtration of water, as described on page 74, is an excellent means for clarifying plain or acidified syrups, since it is indifferent to the action of fruit acids and gives excellent results.