Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/75

Rh, neither soluble in water nor in spirit of wine. By these properties it resembles amber; which has induced some to consider it a mineral bitumen similar to that substance. It yields on distillation an oil, which, like mineral petrolea, is indissoluble in spirit of wine.

Copal itself is soluble in the essential oils, particularly in that of lavender, but not easily in those obtained by expression. It may, however, be dissolved in linseed-oil, by digestion, with a heat very little less than is sufficient to boil it.

A correspondent in the 17th vol. of the Transactions for the Encouragement of Arts, &c. informs us, that copal may be dissolved in spirit of turpentine by the following process: Having prepared a glass vessel, of sufficient capacity to contain at least four times the quantity intended to be dissolved, and which should be high in proportion to its breadth, reduce two ounces of copal to small pieces, and put them into the vessel. Mix a pint of spirit of turpentine with one-eighth of spirit of sal ammoniac; shake them well together; pour them on the powder, cork the glass, and tie it over with a string or wire, making a small hole through the cork. Set the glass in a sand heat, so regulated as to make the contents boil as quickly as possible, but so gently that the bubbles may be counted as they ascend from the bottom. The same heat must be kept up exactly till the solution is complete. It requires the most accurate attention to succeed in this operation; for, if the heat abate, or the spirits boil quicker than is directed, the solution will be impeded, and it will afterwards be in vain to proceed with the same materials; but, if properly managed, the spirit of sal ammoniac will be seen gradually to descend from the mixture, and attack the copal, which swells and dissolves, except a very small quantity. It is of much consequence that the vessel should not be opened till some time after the liquid has become perfectly cold; as it frequently happens that the whole of the contents are blown with violence against the cieling.—The spirit of turpentine should be of the best quality.

The method of dissolving copal in alkohol, is as follows: To half an ounce of camphor, add a pint of alkohol; put it in a spherical glass, with four ounces of copal in small pieces; set it in a sand heat, so regulated that the bubbles may be counted as they rise from the bottom, and continue the same heat, till the solution is completed.

Camphor acts more powerfully upon copal than any other substance. If the latter be finely powdered, and a small quantity of dry camphor rubbed with it in the mortar, the whole becomes in a few minutes a tough coherent mass. The process here described, will dissolve mere copal than the menstruum will retain, when cold. Hence, the most economical method will be, to let the vessel which contains the solution, stand for a few days; and, when it is perfectly settled, to pour off the clear varnish, and leave the residuum for a future process.

Copal will dissolve in spirit of turpentine, by the addition of camphor, with equal facility, though not in the same quantity, as in alkohol.—The vehicle employed in dissolving this resin dries very quickly,