HARDWICKE'S SCIENCE-GOSSIP. 



M5 



GUMS, RESINS, AND BALSAMS. 



By H. DURRANT. 



N the following few 

 notes on several of 

 the better-known 

 gums and resins, 

 I have adopted 

 no systematic ar- 

 rangement. 

 Neither have I 

 said all I should 

 have liked to have 

 said concerning 

 them. But as it 

 was not consistent 

 with the room at 

 my disposal to 

 mention all their 

 various uses, I 

 have suppressed 

 the minor proper- 

 ties and given in 

 as few words as 

 possible the more interesting features. 



I have endeavoured to give the name of the plant 

 producing each variety, together with its uses, native 

 country and other interesting items. 



The distinctions between gums, resins and balsams 

 may be briefly tabulated as follows : 



Resins are the inspissated or thickened juices of 

 plants. They are generally mixed with an essential 

 oil, are insoluble in water, but are soluble enough in 

 either alcohol or the essential oils. Their general 

 characters are inflammability and fusibility. Their 

 ultimate components are carbon, oxygen, and 

 hydrogen. v 



Gtims are soluble in water, but are insoluble in 

 alcohol. 



Balsams or Gum resins contain a quantity of gum, 

 are partly soluble in water, partly so in alcohol, or in 

 other words, they take bo:h alcohol and water to 

 perfectly dissolve them. 



Gum arabic is produced by several species of 

 No. 319.— July 1891. 



acacia. It is quite soluble in water, but in alcohol, 

 ether and oils it is insoluble. It forms an acid 

 solution, as permalate of lime is present. Several of 

 the metallic oxides combine with it. It is very 

 nutritious, so much so that the Arabs who gather it 

 nearly live upon it during harvest-time. We import 

 it from the Levant, Barbary, Senegal, Cape of Good 

 Hope, India, Cairo, &c. 



Gum Senegal the product of Acacia Senegal. This 

 is the best kind of Arabian gum. It is much more 

 clear than gum arabic, sometimes entirely white, in 

 drops as large as a pigeon's egg. Its principal use is 

 in the manufacture of silks, muslins, crapes, &c., to 

 give them the requisite amount of stiffness and glaze. 

 It is also mixed with the colours in caUco printing to 

 give them solidity. 



Gu7n tragacanth or gum dragon. This is obtained 

 from Astralagus ti-agacantha. In appearance it 

 resembles twisted ribbons, of a brownish whitt 

 colour, opaque and rather ductile. When pulverized 

 in a mortar it is of a white colour. The operation of 

 pulverizing is a difficult one, and should be performed 

 in a hot mortar, the gum having been previously heated 

 to 212° Fahr. This gum has a remarkable power of 

 consistence, a small piece swelling up to many times 

 its own size. It has not, however, such a strong 

 power of adhesiveness as gum arabic, but if equal 

 parts of the two be mixed together it forms a nice 

 white gum, very suitable for fastening plants to paper, 

 and other natural history work. The tree is itself a 

 native of Crete. 



Gum sandarach. The product of Callitris quadri- 

 valvis is a native of Barbary. This gum is chiefly 

 used in the manufacture of varnishes, for which it 

 is peculiarly adapted. The Turks employ the wood 

 in the construction of their mosques, it being very 

 tough and possessing great lasting qualities. Im- 

 portation about fifteen tons per annum. 



Barbary gum, a very dark-looking kind produced 

 by the Acacia gufnmifera. In the manufacture of 

 lozenges and confectionery it has valuable qualities. 



H 



