FULLER'S EARTH, so named from its use by fullers as an absorbent of the grease and oil of cloth, a clay-like substance, which from its variability is somewhat difficult to define. (Ger. lV alkererde ; Fr. terre a foulon, argile smectique.) In colour it is most often greenish, olive-green or greenish-grey; on weathering it changes to a brown tint or it may bleach. As a rule it falls to pieces when placed in water and is not markedly plastic ; when dry it adheres strongly to the tongue ; since, however, these prop erties are possessed by many clays that do not exhibit detergent qualities, the only test of value lies in the capacity to absorb grease or clarify oil. Fuller's earth has a specific gravity of and a shining streak; it is usually unctuous to the touch. Micro scopically, it consists of minute irregular-shaped particles of a mineral that appears to be the result of a chloritic or talcose alteration of a felspar. The small size of most of the grains (less than .07 mm.) makes their determination almost impossible. Chemical analysis shows that the peculiar properties of this earth are due to its physical rather than its chemical nature.
The following analyses of the weathered and unweathered condition of the earth from Nutfield, Surrey, represent the com position of one of the best known varieties: (Analysis by P. G. Sanford Geol. Meg., 1889, 6, pp. Of other published analyses, not a few show a lower silica con tent 50%), along with a higher proportion of alumina /o, 23%).
Fuller's earth may occur on any geological horizon, at Nut field in Surrey, England, it is in the Cretaceous formations; at Midford near Bath it is of Jurassic age; at Bala, North Wales, it occurs in Ordovician strata ; in Saxony it appears to be the de composition product of a diabasic rock. In America it is found in California in rocks ranging from Cretaceous to Pleistocene age; in South Dakota, Custer county and elsewhere a yellow, gritty earth of Jurassic age is worked ; in Florida and Georgia occurs a brittle, whitish earth of Oligocene age. Other deposits are worked in Arkansas, Texas, Colorado, Massachusetts and South Carolina.
Fuller's earth is either mined or dug in the open according to local circumstances. It is then dried in the sun or by artificial heat and transported in small lumps in sacks. In other cases it is ground to a fine powder of ter being dried ; or it is first roughly ground and made into a slurry with water, which is allowed to carry off the finer from the coarser particles and deposit them in a creamy state in suitable tanks. After consolidation this fine material is dried artificially on drying floors, broken into lumps, and packed for transport. The use of fuller's earth for cleansing wool and cloth has greatly decreased, but the demand for the material is as great or greater than it ever was. It is now used very largely in the filtration of mineral oils, and also for decolor izing certain vegetable oils. It is employed in the formation of certain soaps, cleansing preparations, pigments for wall-papers, and the finest grade is utilised in toilet requisites.
The name "Fuller's Earth" is applied to a subdivision of the Jurassic rocks of south-west England (see JURASSIC SYSTEM).
(J. A. H.)