"Practically successful purification of water is only attained by allowing frequent access of air to the charcoal, and these filters are specially constructed for this purpose," says the patentee, and there is no objection to it, but the air should be impregnated under pressure to be effective. The features of this system as claimed are: Upward filtration through specially prepared animal charcoal; rapidity with highest purifying power; continuous supply, proper diffusion of water through charcoal; not subject to choke up, and applicable to the largest wants.

Fig. 34. - Rawling's Patent Filter.