This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Bole: a friable earthy substance, uniting with water into a smooth paste, adhering to the tongue, and dissolving as it were in the mouth: of the clayie kind, but more readily imbibing water than the clays strictly so called; when moistened, less viscous and cohesive; more easily diffusible through water by agitations and more freely subsiding from it.
1. Bolus armena. Armenian bole, or bole-armenic: of a pale but bright red colour, with a tinge of yellow; harder, and of a less glossy surface, than most of the other boles.
2. Bolus gallica Pharm. Lond. & Edinb. French bole: of a pale red colour, variegated with irregular specks and veins of whitish and yellow.
Many other bolar earths have been recommended for medicinal uses, and were formerly ranked among the officinals; as, red boles from Armenia, Lemnos, Strigonium, Portugal, Tuscany, and Livonia; yellow boles from Ar-menia, Tockay, Silesia, Bohemia, and Blois; white boles from Armenia, Lemnos, Nocera, Eretria, Samos, Chio, Malta, Tuscany, and Goltberg. Several of these earths have been commonly made up into little cakes or flat masses, and stamped with certain impressions; from whence they received the name of terra sigillatae, or fealed earths. The Armenian and Lemnian have been generally supposed to be the belt, but are rarely met with in the shops: the common French bole, and some bolar earths found in our own country, and even white clay artificially coloured with ochre or colcothar of vitriol, have commonly supplied the place both of those and of the other coloured boles. The substitution of the French to the Armenian, in the several compositions wherein that earth is directed as an ingredient, is now allowed by the London college: and indeed all these earthy bodies, however differing from one another in the degree or species of their colour, or in their texture and compactness, appear, in regard to their medicinal qualities, to be very nearly, if not entirely, alike.
All the boles have for their basis one and the same argillaceous earth; which is not dis-soluble, by the heat of boiling water, in acids, in alkalies, or in any other known menstruum; which, in a strong heat, grows hard, contrary to all the other bodies of an earthy or stony nature, which receive from fire a greater or less degree of friability; and at the same time loses its property of imbibing water, and of being reduced thereby into a tenacious mass. The boles and clays, both in their natural state and when indurated by fire, become dissoluble in part, by strongly boiling them in the concen-trated vitriolic acid, till the more phlegmatic parts of the liquor have exhaled, and the matter remains dry. The compound which the earth, by this process, forms with the acid, is of the same nature with alum: it dissolves in water, and may be crystallized into perfect alum, by adding a suitable quantity of any volatile or fixt alkaline salt to saturate the redundant acid, and after due evaporation setting the liquor to shoot.
The colours of the boles proceed from a flight admixture of a ferrugineous calx; which may be extracted by digestion in spirit of salt or aqua regis, but is Scarcely acted upon by any acid of the vegetable or animal kingdom. Some of them contain a portion of calcareous earth, which is extracted by all acids except the vitriolic, and discovers itself by railing an effer-vescence on the affusion of the acid. The specimens I examined of the bole of Blois gave out a considerable quantity of this earth, those of the common French bole exceeding little, and the Armenian none: possibly, however, different masses of one kind of bole may differ, in this respect, as much as different boles. All the boles seem to participate also of vitriolic acid; which is so intimately blended with the other matter, as not to be separable, or discoverable, without violence of fire.
The ferrugineous calx and calcareous earth are likewise very intimately blended with the proper bolar matter; insomuch, that when the compound is diffused through water, it fettles equally and uniformly without any separation of its parts. If the bole contains any land or small stones, or has been artificially coloured, the sand, stones, and colouring ingredients, separate in the water, and being heavier than the bolar earth, subside before it. On this principle, the boles may be purified from the gritty matter often intermixed among them, and the natural boles distinguished from artificial compositions. The medical virtues of the boles appear to depend on the simple bolar or argillaceous earth. As this earth is not dissoluble by any fluid that can exist in the bodies of animals, it can act no otherwise than by imbibing, or giving a greater degree of consistence to thin sharp humours in the first passages, and in some measure defending the solids from their acrimony. In consequence of this virtue, the boles may be of some service in alvine fluxes, cardialgic complaints, and in some kinds of acute diseases; though they are not possessed, as they have been commonly supposed to be, of any truly astringent, or ab-sorbent, and much less of any alexipharmac powers. The sensation of astringency which they generally occasion, in some degree, in the mouth, seems to consist only in their adhering to and drying the part, by imbibing the fluids that moisten it. Their dose is from fifteen or twenty grains to a dram.