This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Absorbent Earths: distinguishable from other earthy and stony substances by their solubility in acids. Such are, the mineral calcareous earths, as chalk: the animal calcareous earths, as crabs-claws, oyster-fhells, egg-shells, pearl, coral, coralline: animal earths not calcareous, as crabs-eyes and burnt hartshorn. See the respective substances; which have been separately treated of, so far as concerned each in particular; and whose general and common qualities were reserved for this article.
The obvious and immediate virtue of these bodies is, to obtund acid humours in the first passages, and thus to relieve the cardialgic and other complaints occasioned by them: the relief, however, which they afford, is oftentimes only temporary; from their acting only upon the acid already generated, without correcting the indisposition which tends to produce more. If no acid humours are contained in the first pas-sages, these earthy bodies, not soluble by any other kind of fluid, can have no salutary operation; and, by concreting with the viscous contents of the stomach into indigestible masses, may prove injurious in a high degree (a).
(a) Kerr's Account, above quoted.
Absorbents are of more general use in infancy than in adult age; acidities being very familiar to young children, being often in that tender age productive of alarming symptoms, and having a greater or less share in most of their diseases; whereas, in adults, they are much less frequent, accompanying chiefly hypochondriacal affections, cardialgiae, and such disorders as happen in the first passages from the immoderate use of acid and fermentable food.
An hypothesis formerly obtained, which as-cribed the acute diseases of adults to a morbific acid: against which the absorbent earths were introduced as the most direct alexipharmacs. This theory is now justly exploded; these diseases, instead of being produced, being in general most successfully controlled, by acids. The use of absorbents, in different kinds of fevers, is nevertheless still continued, and some-times perhaps with advantage: for, though the earths of themselves are apparently rather injurious than beneficial, yet as acids are often given freely at the same time, the solution of the earth in the acid may prove a medicine more serviceable in particular cases than the acid unobtunded. It is however, doubtless, more advisable, to use the earth previously dissolved in the acid, than to give them sepa-rately.
(a) Vide Tralles Virium terms rentediis ascriptorum examen rigorostius.
The college of Berlin, sensible of the advantage of having the earths, in these cases, previously dissolved, or reduced to a soluble saline form; as well as of the absurdity, retained in other German pharmacopoeias, of precipitating them from their solutions by fixt alkaline salts, and thus rendering them wholly inert; directs them to be digested in distilled vinegar, with a gentle heat, till the menstruum ceases to act, and the filtered solution to be infpiflated to dry-ness. This preparation is greatly preferable to the Ample imbibition with vinegar or lemon juice recommended by some; as by this last management the earth is made soluble only in part, and in an undeterminable proportion.
Solutions of these earths in vegetable acids are in taste somewhat austere. The different earths differ somewhat from one another, both in the degree and in the species of the taste, and probably also in the medical effects, of the solutions: but whether these differences are such, that some of them, as crabs-claws, pearl, coral, and bezoar, are most disposed to promote a diaphoresis in fevers, while others, as egg-shells and oyster-shells, act rather by promoting urine, as seems to be generally supposed, has not been determined by fair experience, the earths having rarely been given in a dissolved or in a soluble state. It is most probable that they all act, when dissolved, as mild cooling restringents; for when given in substance, as absorbents, in cases of acidities, they all tend to restrain fluxes of the belly, or to bring on costiveness, an effect Magifterium solubile, co-ralliorum, perlarum,etc. P. Brandenb, effect to which regard ought to be had in the use of them.
There are two soluble earths, not commonly ranked among the absorbents, whose effects, when combined with acids, are known with more certainty, as they have been used oftener, so combined, than otherwise; to wit, the aluminous earth and magnesia; of which the one is strongly styptic, and the other moderately purgative.
Combinations of the absorbent earths with the nitrous and marine acids are bitterish and of great pungency, particularly those with the marine: the medical effects of these solutions are little known. The vitriolic acid does not dissolve them into a liquid form, but precipitates them from all the others, and is thus combined with them into concretes nearly insipid.
Experiments have been made for determining the comparative strength of different absor-bents, or the quantities of acid they are capable of satiating. Langius reports, that ten grains of crabs-claws destroyed the acidity of forty drops of spirit of salt; that egg-shells, crabs-eyes, and mother of pearl, taken in the same quantity, sa-turated fifty drops each; red coral, white coral, and fixt alkaline salt, sixty drops each; volatile alkaline salt and pearl, eighty drops each; chalk, an hundred drops; oyster-shells, an hundred and twenty; and some lime stones no less than an hundred and sixty (a), These experiments however (admitting their accuracy, and the acid to have been equally neutralized in all, which may be reasonably questioned) do not answer the end so perfectly as could be wished; for, to different acids, the earths have different habitudes; habitudes: from a set of experiments made by Homberg, it appears that oyster-shells, for example, require for their solution more of the marine acid than coral does; whereas of the nitrous acid, contrariwise, the coral requires more than the oyster-shells (a). Neither the nitrous nor the marine acids are those which absorbents are destined to satiate in the human stomach, and by which their strength should be examined: the acids of the vegetable kingdom, and the acid of milk, may be presumed to be the most analogous to such as are generated in the bodies of animals. On trying, with these, the several substances enumerated at the beginning of this article, the differences in their ab-sorbent powers appeared not to be very great: they all saturated pretty nearly the same quantities of the acids; and there remained, from all, quantities very considerable, but not very greatly different, of a matter which further additions of the acid would not dissolve,
(a) Vide Langii Opera omnia medica, Lipsiae 1704, p. 452 & seq.