The various uses of fullers earth may be shortly explain ed. According to the above method, the coarse and fine of one pit are separated ; and the first is used for cloths of an inferior, and the second for those of a superior, quality. The yellow and the blue earths of Surrey are of different qualities naturally, and are, like the above, obtained artifi cially, and used for different purposes. The former, which is deemed the best, is employed in fulling the kerseymeres and finer cloths of Wiltshire and Gloucestershire, whilst the blue is principally sent into Yorkshire for the coarser cloths. Its effects on these cloths is owing to the affinity which alumine has for greasy substances ; it unites readily with them, and forms combinations which easily attach themselves to different stuffs, and thereby serve the pur pose of mordants to some colours ; as is the case in the Turkey red. The fullers generally apply it before they use the soap. It may be used also instead of soap on board of ship, to wash linen or the hands with salt water, with phich it is well known soap does not unite.
The legal restrictions on the exportation of fullers earth, may be found in the 12 Car. 11. 13 and 14 Car. II.; 9 and 10 William III. c. 40 ; 6 Geo. I. c. 21. § 22. The penalties are so enormous, that foreign chemists turned their attention to discover substitutes for fullers earth. Cronstedt describes only the lithomarge of Osmund, Tar tary, and Lemnos ; the Hampshire fullers earth not having come to his hands, probably on account of the severe pe nalties imposed by the English legislature on its exporta tion. Bergman examined them all except the second, which is the keffekil of the Crim Tartars, who are said to use it instead of soap, and of which he was not provided with a sample. Wiegleb, in Crell's Journal, quoted by Kirwan, found that it consists of equal parts of magnesia and silex.
The Lemnian earth, so called as being found in Lemnos, was highly esteemed for many centuries, for its supposed medical virtues, and till lately sold in Europe under the seal of the grand signior, (hence called terra sigillata,) has the external appearance of clay, with a smooth surface, re sembling agate, especially in its recent fractures, which are usually either concave or convex. It may be scraped with the nail, is composed of impalpable particles, though a lit tle gritty between the teeth, under which it feels like tal low. When immersed in water, it is spontaneously divided into small pieces, with a slight crackling noise, but they do not become so small as to be invisible or impalpable ; pul verization and boiling in water diffuse it in the fluid, which passes almost perfectly clear through double filtering pa ,per. This earth removes impurities like soap, though it affords no froth.
The Osmunclic earth comes from Osmund, in the parish of Rutwick, in last Dalecarlia. Its colour is grey like cin
ders; its surface rough, and as if greased ; it is harder than the Lemnian earth, breaks into angular pieces, adheres strongly to the lip, and is more gritty between the teeth than that earth : in water it separates into smaller particles, and is detergent. By the humid analysis, Bergman found the constituent parts of the two foregoing ozn.ths as follows: Amongst the foreign varieties of lithomarge, the fullers, earth of Saxony ought not to be forgotten, particularly in this place, where substitutes are treated of: For this, how ever, we must refer to the beginning of the article, and this head will be concluded by introducing a substance that is very generally found both in Great Britain and abroad. Ful lers earth, we have seen, from the general results, is alit mine, comhined with very fine silex ; it is essential to this earth that the particles of silica should be very fine, other wise they would cut the fine cloth : hence the object in washing over the fullers earth, mentioned in a preceding paragraph. It is owing to the strong affinity, as noted be lore, which alumine has for greasy substances, that it is so useful in scouring cloth ; hence pipe clay, the cimolian earth mentioned in the beginning of this article, is frequent ly used for the same purpose ; and it may also be concluded, that any clay possessed of this property may be considered, in its uses, as fullers earth ; for it is the alumine alone which acts upon the grease in the cloth.
The properties required in good fullers earth are, that it should contribute to the washing away all impurities, and promote that curling and intermixture of the hairs of the woollen cloth, which thicken its texture, and give it the desired firmness. Both probably depend on its detergent quality, that clears away all the unctuous matter of the wool, and renders its parts capable of becoming more perfectly entangled by the mechanical action of fulling ; an effect not so likely to take place where the fibres or hairs are dispo sed by grease to slide easily over each other. The deter gent power resides in all clays, but is doubtless greatly in creased by the siliceous earth, which may be considered as the brush, while the clay serves as the soap. This is fa miliarly shewn by the common practice of adding sand to soap, which renders it much more detergent, but, at the same time more capable of injuring the substances to which it is applied, and that more especially when the sand is coarse. Fullers earth is bad if the sand be not exceewngly fine, and the superior excellence of the Hampshire earth seems to depend more on the fineness of its parts, than on their proportions, as is shewn by the experiment of boiling it in water, alter which it passes more plentifully through the filter than any of the other kinds of lithomarge. (E)