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Gums, Resins, and Their Properties

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114 SCIENTIFIC AMERICAN SUPPLEMENT No. 1677. F1<JBRlJARY 22, 1908. GUMS, RESINS, AND THEIR PROPERTIES. A FEW TECHNICAL SUGGESTIONS. ROSI� is the cheapest and commonest resin (the heres to the varnish and increases its thickness and tine, acetone, and benzol, but not in benzine, gasoline, all term resin is used to designate substances of this consequent ability to resist the solution used for etch­ or naphtha. Asphalt is the best material for lining nature), and is obtained in the distillation of turpen­ ing. Asphalt is used for the same purpose, but the plating tanks or as a stopping-off varnish.-The Brass tine oil from crude turpentine. Three grades of rosin dragon's blood is preferable, as it melts at a lower World. are known to commerce: Virgin, yellow dip, and temperature. hard. The first turpentine that exudes from the tree Gum guaiacum is obtain ell from a tree which grows THE PREPARATION OF GOLD TRI­ after it has been boxed, iil- "virgin rosin." It has a in the West Indies. The tree is cut in the same man­ CHLORIDE FOR PHOTOGRAPHIC light amber color. Yellow dip is the next best grade, ner that a pine tree is treated for obtaining turpentine and the hard is really the scrapings from the tree and the gum exudes. This gum is not extensively PURPOSES. after the turpentine refuses to run. It is very dark used. It is employed to a limited extent in medicine By RA�DOLPH BOLLL,\O. colored. White rosin contains water which renders for the treatment of rheumatism. It is also used in THE double chloride of gold and sodium and aqueous it opaque. If the water is driven off, the rosin be­ the etching of steel knives. Gum guaiacum is soluble solutions of gold trichloride find extensive applica­ comes yellow. in alcohol, and a varnish is produced. This is brushed tion in photography in connection with the toning of The chief uses of rosin are in the manufacture of over the knife and allowed to dry. A rubber stamp is silver prints, in order to reduce the harsh tints to a cheap varnishes, soaps, in the lining of beer kegs and stamped upon a pad of cotton cloth wet with a solu­ more pleasing color. With silver paper giving a visible casks to make waterproof, as a flux in soldering tin, tion of potash and then upon the surface of the steel image, the fixing bath alone gives a picture of an and in various mixtures of greases, belt dressings, and knife coated with the varnish. The rubber stamp has unattractive brick-red or salmon color; but an alkaline adulteration of oils. the design that is to be etched upon the steel. The solution of gold chloride, applied to the print before When rosin is distilled, "rosin oil" is produced. This potash dissolves the gum and leaves the steel bare. fixing, will be r'educed by the silver of the image, is used in the manufacture of printing inks. It is The etching is then done with nitric acid diluted with and the gold will be deposited upon it, changing its also used to adulterate linseed oil. The hard rosin four parts of water. The gum guaiacum is quite solu­ color to a purple or a pleasing bluish black. The most that is dark colored is frequently called "turpentine ble in alkalies, which makes this etching process economical method of obtaining gold salts is to pre­ pitch." Rosin is soluble in turpentine and benzine, possible. pare them from the metal itself. Pure gold is worth but only slightly in alcohol. Gum shellac is produced by the bite of insects upon $20.67 an ounce. It can be easily produced by solution Wood-tar pitch is obtained in the distillation of the branches of certain East Indian trees. The shellac of some alloy of gold and copper in nitro-hydrochloric wood for making wood alcohol and acetic acid. It exudes in the form of drops which cover the insects. acid and the application to this solution of gold and should not be confused with turpentine pitch as it has These drops are collected and melted in muslin bags copper of some chemical reagent that will cause a pre­ more the nature of a coal tar, while turpentine pitch by means of hot water and the insects strained out. cipitation of metallic gold, To begin operations, all if rosin. The melted shellac is poured onto a hot plate, and the the old scrap jewelry that can be collected, such as Burgundy pitch closely resembles common rosin. scales as they occur in commerce are produced. It is settings, wire, pins, old watch cases, etc., which may It is obtained from the Norway spruce and is lighter usually of a brownish-orange color. run from 9 to 18 karats (that is, 24 parts of the alloy in color. It has the peculiar property of combining The bleached shellac is formed by passing chlorine contain 9 to 18 karats of gold) are broken up into into a solid mass withjn a short time after it has gas into a solution of shellac dissolved in borax. The small bits and placed in a pint beaker. About two been broken up. Although quite brittle, it is plastic, shellac is precipitated and then melted and pulled ounces of scrap is a convenient weight to operate on. particularly in summer, and it is impossible to pre­ under water in the same manner that candy is treated. This is covered with a mixture of one ounce of strong serve it for over a few hours in the pulverized condi­ This renders it white and fibrous and removes the ' hydrochloric acid hnd three ounces of strong nitric tion. It soon melts, so to speak, into a solid mass. borax. acid, and the acids allowed to act over night on Gum sandarac is called "gum jupiter," and is ob­ Shellac is soluble in alcohol, and forms a hard, the scrap in a warm place. Solution of the alloy tained from a tree growing in the northern part of quick-drying varnish, extensively used for patterns, takes place without difficulty, and the beaker and its Africa. Its principal use is in the manufacture of var­ varnishing and similar work. It is also used in the contents are now allowed to stand on a water bath nishes. French polishing of wood. The wood is given a large or hot plate heated to about boiling point and thus Gum mastic resembles gum sandarac in appearance number of coats of thin shellac varnish, and each evaporated - fo a thick syrup, very nearly to dryness. and its properties, and is obtained from shrubs which coat is polished or rubbed down before the other is To the contents of the beaker containing chlorides 9f grow along the shores of the Mediterranean Sea. Both applied. In this manner the last coat is very smooth, gold and copper is added hot water, diluting to about gum mastic and gum sandarac are soluble in acetone, although not highly polished ltl,e some other forms of four ounces. Now dissolve about three ounces of fer­ turpentine, and alcohol. Gum mastic is used in var­ varnish. rous sulphate (copperas crystals) in suffi.�ient water to nish maldng. Shellac is soluble in borax, and this solution may make a saturated solution, and add this to the con­ Gum dammar is found in the Moluccas and exudes be used as a varnish or lacquer. At one time it was tonts of the beaker containing the gold and copper from a treo similar to the pine. It is a very light extensively used as a cheap lacquer, but at the�Jresent solution. Metallic gold, having its characteristic lus­ colored gum, and is used for the manufacture of the time it has been entirely replaced by the gun-cotton trous appearance, is precipitated, a ferric salt remain­ lightest colored or transparent varnishes. lacquers. Lacquer made by dissolving shellac in al­ ing in solution. Copper remains in solution. A funnel Amber is not a true gum, as it is not produced by cohol is now used to a limited extent, and is gradually i,; now fitted with a filter paper, and the precipitated any tree or plant at the present time. It is a "fossil being replaced by the gun-cotton lacquers. At one gold collected on it, and washed with hot water until resin," as it was formed in primeval times, probably time it was the only lacquer used, It must be applied it is entirely free of copper and iron salts. The pre­ in the same manner that other gums are now produced. while the work is warm, in order to prevent the ab­ cipitated gold, which has been retained on the filter, Germany produces nearly all of the amber, and it is sorption of moisture by the alcohol and the produc­ is now removed by taking the filter paper out of the cast up on the shores of the Baltic in storms. The tion of a turbidity on the surface. funnel and placing the precipitate in another pint fact that it frequently contains insects indicates that Gum elemi is 9btained from a tree growing in the beaker, adding nitri� and hydrochloric acids, as it was of vegetable origin. The insects became en­ Philippine Islands. It has a white or gray color, and directed in the first treatment, and thus dissolving the tangled in the gum as they are to-day in those which is soft and tough. It is soluble in alcohol. It is used gold again, evaporating to syrup or to such a degree are now found.
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