On the Composition of the Mosaic Gold. 387 



Although the specific gravity is not of itself a sufficient cri- 

 terion, it is found to bear a general relation to the purity of 

 the mineral ; and the Borrowdale and Spanish varieties, which 

 contain the largest proportion of carbon, have the lowest spe- 

 cific gravity. In the same manner, of the Himalayan speci- 

 mens, Nos. 1 and 2, which are the lightest, present the finest 

 grain, and are freest from earthy admixture ; and the speci- 

 mens from Ava and Ceylon approximate to Borrowdale gra- 

 phite, both in weight and external character. None of the 

 specimens of the Himalayan graphite have a metallic lustre 

 unless scraped, and it is then of inferior brilliancy to the other 

 varieties. The smallest nodules have the finest grain, and make 

 the blackest streak : by boiling in oil, the streak is deepened 

 in colour and rendered softer. These nodules are hollow in 

 the centre ; the larger pieces have a slaty fracture, and exhibit 

 a considerable proportion of siliceous admixture. The smaller 

 specimens, deflagrated with nitre, afforded indications of earthy 

 matter, as did the larger in more considerable proportion. 

 The best specimens left a residuum of oxide of iron of 52 per 

 cent ; and about a similar proportion, or 5 per cent, was left 

 after roasting for five hours. There had not been time for a 

 regular analysis, but Dr. A. considers the following as the 

 mineral ogical characters of the graphite of the Himalaya, taking 

 the smaller specimens as a standard. Its colour is charcoal 

 black ; it occurs in rounded and angular fragments ; internally 

 it is barely glistening, externally dull and earthy ; its fracture 

 is very fine grained. The fragments are angular ; its streak 

 is shining and metallic ; it is imperfectly sectile ; it is frangi- 

 ble ; it writes and soils ; it feels rather greasy. The specific 

 gravity is 2*268 to 2*375. — Asiatic Journal. 



ON THE COMPOSITION OF THE MOSAIC GOLD, OR OR-MOLU, 

 DISCOVERED BY MESSRS. PARKER AND HAMILTON. 



The resemblance of this alloy to pure gold has attached to 

 the discovery of it an importance of no ordinary kind. Al- 

 though it is an alloy of zinc and copper, yet great care and 

 experience are necessary to its production. The following is 

 the exact method given by the patentees. 



Take equal quantities of zinc and copper, and melt them at 

 the lowest temperature at which copper will fuse. Having 

 mixed them perfectly by stirring, add zinc in small portions 

 till the alloy in the crucible assumes a yellow colour like brass, 

 then continue adding the zinc till the colour changes to a 

 purple or violet, and becomes perfectly white, which is the 

 colour necessary to its perfection. It may then be cast into 



3 C 2 ingots, 



