Latex and other plant gums

The French cotton plant (Calotropisprocera) is a flowering herbaceous plant that produces latex. When a leaf is snapped, the latex flows freely from the plant tissue.

Latex is a milky-white liquid that occurs in the cells of some flowering plants. It is a complex mixture of substances that may include fats, waxes, and various gum resins. It circulates the plant tissue like sap in branched tubes, conducting other substances and acting as an excretory reservoir. Latex is produced especially by plants of the family Asclepiadaceae, but also by those in the Sapotaceae, Euphorbi-aceae, and several others.

Gums, unlike latexes, are clear, yellow, or amber liquids that harden into translucent solids when exposed to the air. The families Leguminosae, Rosaceae, and Sterculiaceae contain most of the gum-producing trees, which convert cell tissue into gum, probably by enzymic action. In some species, the gum collects in ducts to heal damaged tissue and, in others, such as gum arabic (Acacia senega/), oozes from the bark in response to injury.

Resins are obtained from the sap of various plants; like latex and gums, they consist mainly of hydrocarbons based on isoprene, and their main chemical compound is abietic acid. They may be tapped straight from the tree or collected from the ground, sometimes as fossilized lumps (amber). Shellac is produced from the resinous excretion of a scale insect (Lac-cifer /acca) that feeds on various resin-containing trees, such as the soapberry (Sapindus sp.) and acacia (Acacia sp.) trees of India and Burma. Most resin, however, is tapped from pines, particularly the longleaf pine (Pinus pa/ustris), which grows in the Southeastern United States.

The llareta (Azorella glabra) is a ground-hugging cushion plant that grows high up in the Bolivian Andes. It exudes drops of resin that harden when exposed to the air. Bolivians use the resin as fuel because it produces intense heat when burned.

Natural latex

Most of the commercially used latex is extracted from the Para rubber tree (Hevea brasi-liensis) and is processed into rubber, the subject of the previous article. Other important products derived from natural latex include gutta-percha, balata, and chicle.

Gutta-percha is a yellow or brown leathery material from the latex that is produced primarily by the Paiaquium oblongifolia tree. This tree grows wild and is cultivated on plantations in Malaysia, the South Pacific, and South America. To extract the latex, trees may be felled or rings cut in the bark. On plantations, fresh leaves are chopped, crushed, and boiled in water to remove the latex.

Gutta-percha becomes plastic and water resistant when it is heated. It can, thus, be used as an insulating material. It is employed for underwater electrical equipment as well as for golfballs and chewing gum. Development in synthetic materials, however, has meant that the use of gutta-percha has largely been replaced by products such as polyethylene, nylon, and vinyl resins.

Balata is a hard, rubberlike material made from the milky juice produced by some tropical plants, notably the bully tree (Mani/kara bi-dentata). The trees are grown particularly in Guyana and the West Indies. Balata is often used as a substitute for gutta-percha to make golfballs and belting.

Chicle is said to contain both rubber and gutta-percha and is a pink or brown material consisting of partly evaporated milky sap. The sap is obtained mainly from the Achraszapota tree, which grows in the West Indies, Mexico, and Central America. Chicle was originally developed as a base material for chewing gum, but has been largely replaced by synthetic products.

Some herbaceous plants produce latex, such as the rubber dandelion (Taraxacum kok-saghyz). The roots of this plant, which is widely cultivated in the Soviet Union, are composed of 8 to 10 per cent rubber.

In Portugal, the maritime pine (Pinus pinaster) is tapped for resin. Oil of turpentine is made from distilled resin and is used as a thinner for oil paints and as a solvent.

Plant gums

Gums are soluble in organic solvents, such as alcohol and ether, but they form a gelatinous paste when steeped in water—qualities that have found applications in many industries. The most widely used gum is arabica, which is extracted from the Acacia Senegal. It consists mainly of calcium, potassium, and magnesium salts of arabin (a complex polysaccharide, which, on hydrolysis, yields glucovonic acid and various simple sugars).

Gum arabic has many applications, the most familiar of which are as an adhesive and as the main glue used for postage stamps. It is employed in surgery to bind severed nerves and will maintain blood pressure because it matches the osmotic pressure of blood. The printing industry is a major beneficiary of gum arabic, particularly in lithographic processes where it acts as a demulcent in the preparation of chemical emulsions. This property also makes it useful for thickening inks.

Large quantities of gum are consumed in food and are used in pharmaceutical products. Its sticky texture makes it an excellent binding and thickening agent for lozenges, pills, and candy, and its pleasant smell and consistency also render it a popular additive in a variety of foods and cosmetics. Cum benzoin, which is obtained mainly from the snowbell tree (Styrax benzoin), is used in these products, as is gum tragacanth, which is the dried exudation of the milk vetch (Astralagus sp.).

Resins are used to make a diverse range of products, from paints and varnishes to turpentine and perfume. The pine essence of some resins adds fragrance to numerous household products and the distinctive taste to Greek ret-sina wine. Turpentine, or oil of turpentine, is an aromatic liquid made by distilling resin. It is employed as a solvent and as a vehicle or thinner for oil paints. Some resins have antiseptic properties and are added to cough syrups and mouthwashes.

Amber—a yellowish, usually translucent, fossilized resin from the extinct pine tree Pi-nites succinifera, which once grew along the Baltic coast of Europe—softens when heated and can be fashioned into ornaments and jewelry. It also generates static electricity when rubbed, a property that (from the Greek elek-tron, meaning amber) gave rise to the word electricity. Amber is also produced by tropical trees in Central and South America.

Rosin is the residue from the distillation of the volatile oils of resin. As well as being used for paints and varnishes, it is also applied Jo violin bows and, in a powdered form, is used by ballet dancers and gymnasts to prevent themselves from slipping.

Camphor is a resinous material that is extracted from the camphor tree (Cinnamomum camphora), which grows in Indonesia, China, and Japan. It is steam-distilled from the chopped-up wood of trees, which must be at least 50 years old. Like other resinous products, camphor is used in lacquers and varnishes, but it is also an ingredient in the manufacture of some moth-repellents and explosives.

Amber is fossilized resin and occurs naturally as irregular nodules. It is usually orange or brown in color and may be opaque. This piece of amber (above) was found in the Baltic region of Poland. The insect inside was trapped before the resin hardened.