FULLER'S EARTH is a soft, friable, coarse or fine grained mass of lithomarge clay. Its color is greenish, or yellowish gray ; it is dull, but assumes a fatty lustre upon pressure with the fingers, feels unctuous, does not adhere to the tongue, and has a specific gravity vary ing from 1.82 to 2-19. It falls down readi ly in water, into a fine powder, with ex trication of air bubbles, and forms a non-plastic paste. It melts at a high heat into a brown slag. Its constituents are silica ; 10.0 alumina ; 2.75 red oxide of iron; 1.25 magnesia; 0•5 lime; 24 water, with a trace of potash. Its cleans ing action upon woollen stuffs depends upon its power of absorbing greasy mat ters. It should be neither tenacious nor sandy ; for in the first case it would not diffuse itself well through water, and in the second it would abrade the cloth too much. The finely divided silica is one of its useful ingredients.
After baking it is thrown into cold wa ter, where it tails into powder, and the separation of the coarse from the fine is effectually accomplished, by a simple method used in the dry color manufac tories, called washing over. It is done in the following manner : Three or four tubs are connected on a line by spouts from their tops ; in the first the earth is beat and stirred, and the water, which is continually running from the first to the last through intermediate ones, carries with it and deposites the fine whilst the coarse settles in the first. The advan
tages to be derived from this operation are, that the two kinds will be much fitter for their respective purposes of cleansing coarse or fine cloth; for with out baking the earth they would be unfit, as before noticed, to incorporate so mi nutely with the water in its native state ; it would neither so readily fall down, nor so easily be divided into different quali ties, without the process of washing over. When fuel is scarce for baking the earth, it is broken into pieces of the same size, as mentioned above, and then exposed to the heat of the sun.
The benefit of fuller's earth is mainly. due to the alumina, which, by on the cloth unites with the grease, ing a soap which may either be washed, or may serve as a mordant to fix the lore better on the stuffs. '