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 simply effected by elevating the syrup kettle, since the syrup in its descent to the filter exerts a pressure upon the liquid already in the filter and thus aids rapid clarification. The pressure can be regulated by reducing or increasing the distance between syrup-kettle and syrup-filter, but should not exceed too far, since too rapid filtration reduces it's effectiveness and consequently the brightness and transparency of the syrup. This rapid clarification process can only be carried on in closed filtering apparatus, of which we see a practical one illustrated by figure 412. The syrup when thus put under slight pressure passes more rapidly through the clarifying substances employed and accumulated on the filter, while, if ordinary filter bags are used, the liquid may absolutely stop passing; therefore subsidence is in the latter case resorted to, previous to filtration.