RESINS. Resinous bodies form a very numerous class of vegetable substances. When volatile oils are exposed to the air, they become thick after a shorter or longer time, and are then found to he converted into a resin. The oil absorbs oxygen from the air, and is deprived of part of its carbon, which combining with the oxygen of the atmosphere, forms car bonic acid. Resinous substances, there fore, are generally considered as volatile oils saturated with oxygen. The gene ral properties of resinous substances are the following. They are solid, brittle, and commonly of a yellowish colour, with some degree of transparency. The taste, resembling volatile oils, is hot and acrid. They have no smell. The specific gravity is from 1.01 to 1.22. All resinous bodies are electrics, and when excited by friction, the electricity is negative ; hence it is called resinous electricity. They melt by being exposed to beat, and burn with a yellow flame, giving out a great quantity of smoke. Resins are insoluble in water. Resinous substances are solu ble in nitric acid ; part is precipitated by the addition of water, and the whole by means of the alkalies. With the assist ance of heat they are all soluble in alco hol, and in sulphuric ether. Resins are soluble in some of the fixed oils, and also in volatile oils. Resinous substances have been found to be soluble in the fixed alkalies. We shall enumerate some of
the resins which are best known, and which have not already been described in separate articles.
Eosin. This substance is extracted from different species of the fir, and the resinous matter obtained from it has re ceived different names. That procured from the pinus sylvestris is the common turpentine ; from the pinus larix, Venice turpentine ; and from the pinus balsamea, balsam of Canada. The turpentine is ob tained by stripping the bark off the trees ; j a liquid juice flows out, which gradually hardens. This juice consists of oil of turpentine and rosin. By distilling the turpentine the oil passes over, and the rosin remains behind. By distilling to dryness common rosin is obtained. When water is added, while it is yet fluid, and in corporated by agitation, what is called yellow rosin is formed.
Pitch is a resinous juice obtained from the pinuspicea, pitch pine. It is purified by melting and squeezing it through linen bags, and it is then known by the name of white, or Burgundy pitch. White pitch mixed with lamp-black forms black pitch.
Sandarac. This resinous substance is extracted from the juniper. It is a spon taneous exudation from this plant in the form of brown tears, which are semitrans parent and brittle. See BALSAM, COPAL, Gosicuar, &c.