Linseed, or flaxseed, oil is obtained by expression from flaxseed. It is a thick mucilaginous oil, when first extracted, called _raw_ oil, and in this state, is seldom used. The preparation, it undergoes before it is used as drying oil for mixing with paints, is nothing more than boiling it with litharge, or some oxide of lead, which separates the mucilage, and unites with the oil. By this treatment, it acquires the property of drying with facility, when exposed to the atmosphere. Linseed oil unites with great ease with oils, tallow, fat, wax, &c. Some of these compositions are used in fire-works. A preparation of pitch, mutton suet, and linseed oil is used, for instance, in preventing the access of moisture to fuses; and in military fire-works, it is employed in combination with pitch, rosin, mutton suet and turpentine for incendiary works. Wax, and tallow, we may here add, are also used in the preparations of similar works. _Sec. LI. Of Gum arabic, and Gum Tragacanth._ Gum arabic, which exudes from a tree that grows in Egypt and Arabia (_Mimosa nilotica_) when pure is transparent, and nearly colourless. There are several varieties of this gum; the _gum senegal_, for instance, which is of a reddish colour, and occurs in larger pieces. Other mucilaginous substances, the peach tree gum, the cherry tree gum, &c. which exist only in small quantities, are analogous to the gum of the Mimosa. Gum arabic is brittle, and for that reason may be easily reduced to powder. It is readily dissolved in water, with which it forms mucilage. In this state, it is employed in fire-works, chiefly as a vehicle for the mixing of pastes, matches, &c. Gum is a vegetable oxide, composed of carbon, hydrogen, and oxygen. It does not crystallize. It is precipitated by some metallic salts, as acetate of lead. It is insoluble in alcohol, which distinguishes it from resins. Nitric acid decomposes it, and changes it into the saclactic or mucous acid. With sugar, the same acid produces oxalic acid. Gum tragacanth, or gum dragon, is the produce of a thorny shrub, which grows in Candia, and other islands of the Levant, called _astragalus tragacantha_. The gum obtained from this shrub has many properties in common with gum arabic, and is, therefore, used as a paste. It dissolves readily in boiling water; but is insoluble in alcohol, or ether. It consists, almost entirely, of a peculiar vegetable principle, which is called _cerasin_ by Dr. John. Cerasin has the adhesive qualities of gum arabic, but in a greater degree. It is said to constitute a part of the gummy matter, that exudes from the _prunus cerasus_, _prunus avies_, _prunus domestica_, &c. _Sec. LII. Of Cotton._