Synonyms.—Infusorial Earth; Diatomaceous Earth.
Kieselguhr is a siliceous deposit, formed chiefly of the frustules and fragmentary debris of diatoms—minute unicellular plants—which have accumulated in the depths of lacustrine districts. Immense beds, from 40 to 50 feet deep, occur in Virginia, also in Germany, Aberdeenshire, and elsewhere. Specimens from different localities vary considerably, not only in appearance but in the matters with which the diatomaceous residue is associated. In its natural state the deposit contains varying proportions of organic matter (½ to 20 per cent.) as well as sand, clay, and iron oxide. For pharmaceutical use, it should be incinerated to destroy all organic matter, washed with hydrochloric acid, then with water, and dried. In this state it consists of practically pure silica. Kieselguhr occurs as a whitish, or slightly buff-coloured, fine, gritty powder, which is odourless, tasteless, and unaffected by all ordinary solvents. It should not char nor give off any unpleasant odour on ignition and hydrochloric acid with which it has been shaken should leave no residue on evaporation. Under the microscope it is seen to consist of various forms of diatomaceous skeletons.
Uses.—Kieselguhr is used similarly to white fuller's earth in the preparation of absorbent and emollient dusting powders, usually with boric acid and zinc oxide or oleate. It is much employed as a basis for disinfectant powders and for dentifrices—powder or paste—containing carbolic or boric acid. It is a valuable absorbent for use as a pill excipient with volatile oils, and liquefying mixtures (e.g., menthol and carbolic acid), the mass being prepared with hydrous wool fat or glycerin of tragacanth. Kieselguhr is also used as a filtering medium, to clarify syrups and other liquids; for this purpose the powder should be triturated in a mortar with a little of the liquid before being added to the bulk of liquid to be filtered. It absorbs three times its weight of nitro-glycerin, and is used for that purpose in making dynamite. A variety of kieselguhr is known under the trade-name Dimatos.