This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
The salts of the leaves and other herbaceous parts of plants are more difficultly brought to a state of perfect purity than those of the more woody and compact; a portion of oily matter being tenaciously retained, minute indeed, yet sufficient to give a brownish tinge. A salt of this kind is generally prepared, or expected to be prepared from wormwood, sometimes from broom, and sometimes from bean stalks, all which are sufficiently well adapted to this use, their allies yielding as large a proportion as molt of the common herbaceous matters, and their salt seeming to be almost merely alkaline, or free from any considerable quantity of the other kinds of saline matter, of which the ashes of some vegetables contain more than they do of alkaline salt. About London, the shops are usually supplied from the country with the ashes of wormwood ready burnt; but that more of the oil may be consumed than the simple burning little water, and saturated with any convenient acid, a8 diluted spirit of salt: the point of saturation is readily and accurately obtained by means of stained paper, as directed in page 19. For the greater facility in trials of this kind, a quantity of the spirit of salit may be so diluted, that six-teen drams of it for instance may exactly saturate the one dram of pure alkali. If then a solution of one dram of any given salt be saturated with the same acid liquor, so many drams or parts of a dram of the acid as are required for the saturation, so many sixteenths or parts of sixteenths of pure alkali does the given salt contain. This appears to be the most simple and commodious, as well as the most accurate way, that has yet been contrived, for determining the alkalicity, or degree of purity, of all kinds of lixivial salts.
Sal abfinth, of the herb has dissipated, they are further calcined with a red heat, and occasionally stirred, for some hours: the white ashes are then boiled in water, and the filtered lye evaporated to dryness.
Some have endeavoured to retain in the salt as much as possible of the oil, by burning the plant with a close srnothering heat, continued no longer than till it is reduced fully to ashes: that is, till the alkaline salt is generated, for these salts do not appear to exist naturally in vegetables. The alkalies thus prepared are of a dark brown colour, and supposed to be much milder and less acrimonious, and more of a saponace- ous nature, than those which have been farther diverted of oil. But as we now have, in the soda or natron, an alkali as mild as can be wish-ed for, this inelegant, precarious and unfrugal method of suppressing the acrimony of the common alkalies, becomes unnecessary.
Among all the known vegetables, or vegetable productions, there are none from which a pure alkaline salt is obtainable so easily, and in so large a quantity, as from tartar. If red or white tartar be burnt with a moderately strong fire, either in a proper vessel, or wrapped up in wetted brown paper, to prevent the smaller pieces from dropping down through the interstices of the coals on being first injected into the furnace, it soon turns to white ashes, which yield on the first elixation a strong fiery salt †, of a snowy whiteness, amounting to about one fourth the weight of the tartar. The strength of the salt is somewhat further increased, by keeping it melted for some hours in an intense fire; in which operation, if the crucible cracks or is left uncovered, so as that the flame may have any access to the salt, or if a minute portion
† Sal tartari Ph. Ed, tion of any inflammable matter is introduced, it assumes, in part at least, a greenish or blue colour, which is commonly looked upon as a mark of its srength. - A pure and strong alkaline solution is obtained, by exposing to the air, in a moid place, either the salt, or the white ashes‡ of tartar: the alkali imbibes in a few days so much of the aereal moisture, as to run wholly into a liquor, leaving, how highly soever the salt has been purified before, a considerable quantity of earthy matter. If the liquor be infpiffated to dryness, and the dry salt again deliquiated in the air or dissolved in pure water, an earthy matter is still left: and even if the filtered solution be kept for a length of time in a close stopt glass vessel, an earthy substance gradually separates and falls to the bottom.
Alkaline salts are prepared for common uses, in the way of trade, chiefly from wood; of which, in the forests of Germany, Russia, and Sweden, large piles are burnt on purpose. To save the trouble of boiling down the lye, the finer part of the ashes unelixated is in some places tempered with it into the consistence of mortar, which is afterwards stratified with some of the more inflammable kinds of wood, and burnt a second time: in others, the lye is soak-ed up in dry straw, and this drained and burnt. The impure saline masses, obtained by these or similar methods, are called Potashes; the strong-ed of which has been generally reckoned that brought from Russia (Cineres ruffici) in dark-coloured hard masses, of a very pungent taste, yet containing so much earthy matter as not readily to liquefy or grow moist in the air. This potash is said to be prepared in the first of the ways above-mentioned: but it appears from some late experiments, that another ingredient is made use of in the process; the masses, as brought to us, being found to contain more quicklime than alkaline salt (a), and on this depends the great strength and corro-siveness of the Russian potash. For a purer salt, the lye is boiled down in large iron ves-sels; and the dark-coloured dry salt, which concretes into a hard crust on the sides and bottom of the vessel, is beaten off with a mallet and chisel, and calcined in an oven, with a gradual fire, till it becomes white; in which state it is called, from its pearly appearance, pearl-ash. For some years pad, we have been supplied chiefly from our American colonies, with compact alkaline masses, much more pure that the above pot-ashes, though less so than the pearl-ash; prepared by boiling down the lye to dryness, and then increasing the fire till the salt becomes red-hot, and melts, so as to be conveniently laded out with iron ladles: the troublesome operation of getting off the indurated salt from the boiler is thus avoided; and the strong melting heat, though of short continuance, supplies in great measure the tedious calcination of the salt; for though the inflammable matter, on which the colour depends, is in fusion not consumed, it is burnt to an indis-soluble coaly state, so that lyes made from these melted potashes with water are nearly as colour-less as those of the whitest pearl-ashes. * The college of Edinburgh, which has discarded the oily alkalies of wormwood, broom, etc. now directs a pure incinerated alkali to be made from pearl-ashes, first burned with a red heat in a crucible, then dissolved in water, cleared by subsidence, and evaporated to dryness in an iron pot. This salt will dissolve in equal its weight in water, and the solution is analogous to the former oleum tartari per deliquium. The London college, in their last pharmacopoeia, have given the specific apellation of kali to the fixed vegetable alkali, in all its varieties; and they order it to be got pure from pearl-ashes, or any other vegetable allies, by lixiviation in water, colature, evaporation to a pellicle, sepa-ration of the neutral salts which will then crystal-lize, and laftly, evaporation to dryness. It is also allowed to be similarly prepared from burned tartar. For a liquid preparation, this pure salt is set apart in a moist place till it spon-taneously deliquesces.