534 



GAMBOGE 



of two or throo days. Two quarts of tho saturated solution are added to 300 or 400 

 gallons of tho water contained in tho bath. Over tho bottom of tho bath is first spread 

 a thin layer of finely-granulated zinc, then a cleaned iron plate, and so on, a layer of 

 granulated zinc and a cleaned iron plate alternately, until tho bath is full ; the zinc 

 and iron, together with tho fluid, constitute a weak galvanic battery, and the tin is 

 deposited from tho solution so as to coat the iron with a dull uniform layer of metallic 

 tin in about two hours. 



The tinned iron is then passed through a bath containing fluid zinc, covered with 

 sal-ammoniac mixed with earthy matter, to lessen the volatilisation of the sal-ammo- 

 niac, which becomes as fluid as treacle. Two iron rollers immersed below tho sur- 

 face of the zinc are fixed to the bath and are driven by machinery to carry the plates 

 through the fluid metal at any velocity previously determined. Tho plates are received 

 one by one from the tinning bath, drained for a short time, and passed at once, whilst 

 still wot, by means of tho rollers, through the bath as described. Tho plates take up 

 a very regular and smooth layer of zinc, which, owing to the presence of tho tin 

 beneath, assumes its natural crystalline character, giving tho plates an appearance 

 resembling that known as the moiree metalliqiie. See Hunt's Handbook to the Great 

 Exhibition. 



It is stated that galvanised iron plates cut with shears so as to expose tho central 

 iron become zinced round tho edges, and at the holes where tho nails were driven. 

 We are also informed that ungalvanised iron will, if moist when near galvanised 

 plate, become zinced, and that telegraph wires, where cut through, become coated by 

 the action of the rain-water on the galvanised portion of the surfaces. 



It has been stated that tho galvanised iron is not more durable than unprotected 

 iron ; that, indeed, where the zinc is by any accident removed the destruction is more 

 rapid than ordinary. We have made especial enquiries, and find that in forges where 

 there is any escape of sulphur-vapour tho galvanised iron does not stand well ; but 

 that under all ordinary circumstances it has the merit of great durability in addition 

 to its other good qualities. 



GAXiVAiro-PXf ASTXC. The German name of Electro-metallurgy. See Eo:c- 



TfiO -METALLURGY. 



GAMBXR, or GAMBXER. Tho Malayan name of an extract obtained from the 

 Uncaria Gambier. It is the Terra Japonica of tanners. 



Two methods of obtaining gambir aro described : one consists in boiling the loaves 

 in water, and inspissating the decoction ; the other, which yields tho best gambir, 

 consists in infusing the leaves in warm water, by which a fecula is obtained, which is 

 inspissated by the heat of the sun, and formed into cakes. The best gambir is made 

 at Ehio, in the Isle of Brittany, in the Eastern Archipelago ; and tho next best is 

 that of Lingin. It is principally imported from Singapore, and is used principally for 

 tanning, tinder the name of Terra Japonica. The Mimosa catechu yields a different 

 extract from the gambir, but catechu and gambir are ofton confounded. 



GAMBXR CATECHU 1 . See CATECHU. 



GAMBOGE. (Gommc gutte, Fr. ; Gutti, Gor.) Gamboge appears to have 

 been first brought from China in 1603, and its oriental name was said to bo 

 Ghittaiemon. 



It is generally supposed to bo produced from tho Hebradendron cambogioidcs of 

 Graham and tho Xantlwchymus ovalifolius of Roxburgh ; but different kinds of 

 gamboge appear to havo different botanical sources, several species of Garcinin nnd 

 Cambogia yielding this substance. In Ceylon tho gamboge is obtained by wounding 

 tho bark of tho tree in various places with a sharp stone, when tho flowers begin to 

 appear. Gamboge is imported from Siam, by way of Singapore and Penang. It is 

 known in three forms : in rolls or solid cylinders ; in pipes or hollow cylinders ; in 

 cakes or amorphous masses. Gamboge in small quantities is also obtained in Ceylon. 

 Gamboge consists of resin, 74-2; soluble gum. 21'8 ; moisture, 4'8. 



