1897.] 



on Diamonds, 



483 



The diamond has a peculiar lustre, impossible to mistake. On 

 the sorting table the stones look like clear pieces of gum arabic, 

 but with an intrinsic lustre which makes a conspicuous shine among 

 the other stones. 



Watching the white men in the sorting room is an experience but 

 tame compared to the excitement of taking a sorter's place at the big 

 diamond table and disinterring from the gravel diamonds usually 

 described as the iinest and biggest found for many a day. The 

 interest, however, abates when the amateur sorter is told that the 

 jewels may not be carried away as mementos ! 



Sometimes as many as 8000 carats of diamonds are separated in 

 one day, representing about 10,000Z. in value. 



Diamonds occur in all shades, from deep yellow to pure white 

 and jet black, from deep brown to light cinnamon ; they are also 

 green, blue, pink, yellow, orange and opaque. 



From the pulsator sorting room the stones are taken to the 

 Diamond Office to be cleaned in acids and sorted into classes by the 

 valuators, according to colour and purity. It is a sight for Aladdin 

 to see the valuators at work in the strong-room of the De Beers 

 Company at Kimberley (Fig. 14). The tables are literally heaped 

 with stones won from the rough blue ground — stones of all sizes, 

 purified, flashing and of inestimable price ; stones that will be 

 coveted by men and women all the world over ; and last, but not least, 

 stones that are probably destined to largely influence the development 

 and history of a whole huge continent. 



When the diamantiferous gravel has been washed down to a point 

 at which the stones can be picked out by hand, a good plan for 

 separating them is by their specific gravities. The following table 

 ^ives the specific gravities of the minerals found on the sorting tables. 

 I have also included the specifi.c gravities of two useful liquids. 



This table shows that if I throw the whole mixture of minerals 

 into methylene iodide, the hornblende and all above that mineral will 

 rise to the surface ; while the diamond and all minerals below will 

 sink to the bottom. If I take these heavy minerals, and throw them 

 into thallium lead acetate, tliey will all sink except the diamond, which 

 floats and can be skimmed ofi". 



Hard graphite 

 Quartzite and granite 



Beryl 



Mica 



Hornblende 

 Methylene iodide .. 



Specific 

 Gravity. 

 , 2-5 

 , 2-6 

 2-7 

 , 2-8 

 , 3-0 

 , 3-3 



Diamond 3' 5 



Specific 

 Gravity. 



Thallium lead acetate .. 3*6 



Garnet 3-7 



Corundum 3" 9 



Zircon 4*4 



Barytes 4*5 



Chrome and titanic iron ore 4 • 7 



Magnetite S'O 



In illustration, I have arranged an experiment. In front of the 

 lantern is a cell containing a dense liquid ; when I throw into it 

 several minerals of different specific gravities, some sink whilst 



