This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Copal: supposed to be a resinous concrete, obtained from certain large trees growing in New Spain; more probably a mineral bitumen, analogous to amber.. It is brought to us in irregular mafies; some of which are trans-parent, and of all the intermediate shades of colour from a very light yellow to a gold colour and a deep brown; others are whitish and semitransparent.
Pulv. con-trayerv. comp. Ph. Lond.
semitransparent. In the middle of some of the masses is found a cavity containing some drops of a clear saline liquor: in others, infects and vegetable matters are inclosed(a).
These concretes, however various in ap--pearance, are in quality very nearly if not entirely alike. They have a more agreeable smell than srankincense, to which some have resembled them, and when laid on a red-hot iron, they do not melt so thin, or burn away so sad. They do not soften in the mouth on being chewed, like anime, with which they have been confounded by others. From those, and from all the other known resinous bodies, they differ more remarkably, in being exceeding difficultly dissoluble in rectisied spirit of wine, and yielding in distillation an oil which like the mineral petrolea is also indissoluble in spirit; in being readily dissolved by the concentrated vitriolic acid, and essential oils, not by expressed oils, or volatile or fixt alkalies. Though pure spirit of wine, by moderate digestion, seems to have little action on copal; a boiling heat, or long agitation, enables it to take up a considerable portion: the undissolved part is tenacious and white: the filtered solution is of a gold yellow colour, in taste at first sweetifh, afterwards agreeably aromatic, inclining to bitter. It is said that spirit of wine saturated with camphor dissolves the copal more easily than pure spirit. The medicinal effects of this bitumen are not much known, as it has never been much in use: it is recommended as a warm corroborant; and may be presumed to be similar to amber.
(a) Memoires de l'acad. roy. des scienc. de Berlin, pour l'ann. 1758.