140 



HARDWICKE'S SCIENCE-GOSSIF. 



It calls for no special comment. We import it from 

 the Morocco coast. 



Gum gedda, an inferior quality of the foregoing. 

 Reddish colour. 



Canada balsam. This is supplied by the Abies 

 balsamifera. It is contained in blisters in the bark. 

 The blisters are punctured, and the balsam is 

 collected as it exudes. This is a most useful sub- 

 stance, being in great demand in a number of manu- 

 factures, &c. It is used in cementing lenses together. 

 In microscopy comment is needless, but besides 

 being an excellent preservative, it gives great trans- 

 parency to the object. We import nearly all of it 

 from America. 



Gitaiaaim. This resin exudes from the Giiaiacum 

 officifiale, a native of Jamaica and the surrounding 

 islands. A piece of paper treated with tincture of 

 guaiacum takes on a green tint under the violet rays, 

 when exposed to the prismatic spectrum, through 

 oxidization. Red rays destroy the colour. Solu- 

 bility, 90 per cent, in absolute alcohol. Lignum vitse, 

 the hardest and heaviest wood known, and which 

 sinks on being placed in water, is the timber of this 

 tree. 



Copal. This is the product of several leguminous 

 plants in Africa, East Indies, South America, and 

 Australia. It is generally seen in large angular 

 lumps, often as large as a hen's egg, of a bright 

 yellow colour, and very transparent. The African 

 variety is of a darker colour, and not so transparent ; 

 its surface appears dusty. The Australian is the 

 largest. That from the East Indies is the product 

 of Hymencza coiirbaril. In lumps sometimes nearly 

 sqiiare and generally covered all over with slight 

 indentations. It is known as gum anime. Chiefly 

 used for fine varnishes. 



Guj7t mastic^ the product of Pistacia lentiscus. In 

 small ovoid and round tears about the size of a pea 

 and rather flattened. The tree is a native of Chio 

 and Northern Africa. To obtain the resin the bark 

 is cut transversely, after which the mastic exudes in 

 small drops and either hardens on the bark or falls 

 to the ground. That which falls to the ground is 

 the inferior quality. It has a fragrant smell, and is 

 much used by the Turkish ladies in their toilet. A fine 

 varnish is made from it. Dentists also use it for 

 stopping hollow teeth. About ten or twelve tons are 

 imported annually, mostly from the Levant. 



Gtim dammar: this is a light-coloured substance 

 which is obtained from the Piniis dainmara, native 

 in India, from whence it is exported. It is very useful 

 in making varnishes, especially photographic. It is 

 soluble in benzole, only partly so in alcohol, and is 

 used sometimes as a substitute for Canada balsam. 



Gutn gamboge: a product of Hedyadendro7i gam- 

 bogioides, native on the Malabar coast and in Ceylon. 

 It is a gum resin, and is obtained by puncturing the 

 bark of the tree when the flowers begin to appear. 

 We know it best by its appearance in amorphous 



masses, but it also takes the form of hollow rolls and 

 solid cylinders. The best hollow rolls come from 

 Siam. From this gum the beautiful yellow colour of 

 gamboge is manufactured. 



Gtdta-percha : the inspissated juice of Isonandra 

 gutta. When freshly gathered it is rough, dry, 

 slightly soluble and very inflammable. To render it 

 fit for use it is immersed in boiling water ; this 

 softens it and makes it capable of being moulded into 

 any shape, which it retains when cold. 



The juice is found between the bark and the 

 wood. Its uses are too numerous to specify, many 

 being too well known. 



Caoutchouc, india-rubber, is the product of many 

 euphorbiaceous plants. We get most of it from the 

 Brazils and Central America. In Brazil it is 

 obtained from the Siphonia elastica, which grows to a 

 height of between fifty to sixty feet ; and in Central 

 America it is obtained from Castilloa elastica. Most 

 of that we now use comes from Central America, 

 where the juice is simply collected into cups, from 

 incisions made in the bark. To coagulate the milky 

 juice and convert it into rubber fit for exportation, 

 the juice of a vine called "achuca" is mixed with it 

 and so powerful is its action that five or six minutes 

 is sufficient to produce coagulation. The Brazilian 

 method slightly differs. The juice is first collected 

 in clay bowls, it is then smeared over various shaped 

 moulds, made also in clay and taking the form of 

 bottles, balls, spindles, &c. Successive coats are 

 laid on, each one having previously been allowed to 

 thoroughly dry; either in the sun or in the smoke of 

 a fire, which blackens it. When a sufficient thickness 

 is obtained, the clay is washed out leaving the india- 

 rubber ready for exportation. The trees yield 

 twenty or thirty gallons of juice, and when we con- 

 sider that each gallon will produce two pounds of 

 market india-rubber, the harvest is not so bad. 

 Other trees producing caoutchouc are Siphonia 

 brasiliensis, S. hitea, and S. brevifolia. 



Dextrine, British gum, torrified starch. To pro- 

 duce this gum, starch is heated until vapour rises ; by 

 this procedure the starch becomes soluble both in 

 cold^and hot water, and all its gelatinous character 

 disappears. It can also be made by moistening 1000 

 parts of dry starch with very dilute nitric acid. It is 

 formed in small blocks and dried in the open air, 

 afterwards being placed in an oven heated to 152°. 

 After this they are pulverized and again dried by 

 heat. In colour dextrine is pale yellow ; insoluble 

 in alcohol, more flexible and not so brittle when dry 

 as gum. Dextrine and starch have the same 

 chemical composition CgHjoOs. The gum on the 

 back of postage stamps is dextrine. 



Turpentine. This valuable fluid is the product of 

 several trees, principally Pinus pahistris and P. tceda. 

 Most of it comes from the United States, generally 

 in large barrels, of the consistence of treacle or honey. 

 The oil is obtained by distillation and the remainder 



