GUM RESINS

( Gomme-résines , Fr.; Schleimharze , Germ.) When incisions are made in the stems, branches and roots of certain plants, a milky juice exudes, which gradually hardens in the air; and appears to be formed of resin and e ential oil, held suspended in water charged with gum, and sometimes with other vegetable matters, such as caoutchouc, ba orine, starch, wax, and several saline matters. The said concrete juice is called a gum-resin; an improper name, as it gives a false idea of the nature of the substance. They are all solid; heavier than water; in general opaque and brittle; many have an acrid taste, and a strong smell; their colour is very variable. They are partially soluble in water, and also in alcohol; and the solution in the former liquid seldom becomes transparent. Almost all the gum resins are medicinal substances, and little employed in the arts and manufactures. The following is a list of them: Asa-fœtid a; gum ammoniac; bdellium ; euphorbium; galbanum ; gamboge ; myrrh ; olibanum or frankincense; opoponax ; and scammony. Some of these are described in this work under their peculiar names.