44° New Facts concerning the Diamond. [October 



whose weight sometimes amounts to several decagrammes, 

 has not yet been discovered at the Cape of Good Hope, 

 although the attention of the diamond seekers has been 

 especially directed towards this apparently worthless sub- 

 stance ; it may be therefore inferred that it does not exist 

 in the diamandiferous alluvium of that locality. An 

 examination of two small black fragments, sent from the 

 Cape as supposed carbonado, showed that they contained no 

 carbonado whatever, but consisted almost entirely of hydrated 

 oxide of iron. 



In addition to carbonado and to the ordinary diamond, 

 there exists another variety, distinguished by lapidaries 

 under the name of boart. The appearance of this is usually 

 spheroidal, translucid — but not transparent — and colourless, 

 or of a greyish tint : it cannot be converted into octahe- 

 drons by cleavage, and, moreover, it is much harder than the 

 crystallised diamond, yielding, however, in this respect to 

 carbonado. On account of their greater hardness, carbonado 

 and boart are employed almost entirely in the composition 

 of the powder used in diamond cutting, such powder being 

 greatly preferred by the lapidaries to that formerly in use, 

 which was obtained from well crystallised diamond. 



It was thought that crystalline boron, which for some 

 years has been obtainable by artificial means, w r ould equal 

 or even surpass the diamond with respect to its hardness, 

 and might therefore be applicable to the working of 

 diamonds, but the question remains an open one ; the high 

 price of the substance in question being opposed to its 

 employment. 



As regards the density of the diamond, many data 

 exist, which, however, show many discrepancies. The 

 number 3'520,5 was observed by Thompson, at a tem- 

 perature which is not indicated; M. Halphen found the 

 density of the celebrated diamond, known as the " Star of 

 the South," to be 3*529 at 15 C. M. Schrauf, operating 

 upon the Florentine diamond belonging to the crown of 

 Austria, obtained the number 3*5143, as a mean of two 

 experiments whose results corresponded but little, and after 

 correction for the weight of air, water at 4 C. being taken 

 as unity. A series of experiments were made by M. Schrotter 

 upon different diamonds, among which were always several 

 which were at the same time coloured, and imperfectly 

 transparent, and others which were traversed by fissures. 

 After making the necessary corrections for the w r eight of the 

 air, the average density of the diamond was found by this 

 gentleman, when compared with that of water at 4°C, to be 

 3'5i432. 



