202 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



The earlier methods of extracting diamonds from the rock when excavated, 

 were as primitive as were those first adopted for mining the rock. It has been mentioned 

 above that the dry diggings are situated on an arid plateau, and at the time of their first 

 discovery the water required for every purpose had to be fetched from the Vaal River, many 

 miles away. This necessity forbad the washing of the diamantiferous material as was 

 practised at the river diggings. The mass had therefore to be coarsely broken up with 

 wooden pestles and the coarse and fine material separated by sieves ; the material of medium 

 grain was then, as in the river diggings, spread out in a thin layer on a sorting-table, and 

 any diamonds it contained picked out by hand. 



By this method all the stones which passed through the fine sieve, the mesh of which 

 was about ^ to ^-g inch, were of course lost, these smaller stones being not then considered 

 worth the time and trouble involved in their collection. The larger rock-fragments 

 separated by the use of the coarse sieve with a mesh of f to f inch were thrown aside, 

 though many would of course contain diamonds. It is estimated that during the period in 

 which these methods were practised, at least as many diamonds were overlooked as were 

 found, and in 1873 the debris was reworked and yielded a rich harvest. The material taken 

 from the richest part of the mine has been worked over even a third time, and thanks to 

 the use of improved methods, the result amply repaid the workers for their trouble. 

 Hundreds of poorer miners, who were not fortunate enough to possess a claim, gained a. 

 living by working over the material of old mine heaps, as is still done at some places in 

 India. 



The lack of water was not felt for long ; very soon a main 18 miles long, bringing 

 water from the Vaal, was constructed, and this supply was further supplemented by the 

 numerous springs in the district, and by the water pumped out from the mines themselves. 

 Thus it soon became possible to treat the diamantiferous material gi the same way as at the 

 river diggings, and so the term dry diggings came to be a misnomer. At first, the " blue 

 ground " was reduced to fragments and then washed by the aid of the same simple appli- 

 ances as had been in use at the river diggings. Improved methods, however, were 

 gradually introduced ; thus in 1874, a washing machine worked by hand was employed for 

 the first time, and this in 1876 and 1877 was itself replaced by-a machine driven by steam. 

 The construction of this was so much improved that it was capable of dealing with almost 

 two thousand times as much material as could formerly be treated by washing, and of 

 collecting stones which, on account of their small size, had formerly been lost. The 

 diamonds are picked out by hand from the heavy residue, and are finally freed from any 

 foreign matter which may adhere to them, by treatment with a mixture of sulphuric and 

 nitric acids, after which they are ready for the market. 



The " blue ground " excavated from the deeper parts of the mine is too hard and 

 compact to be washed without previous treatment. It is therefore spread out in thin layers 

 on the hardened gi-ound of large fenced-in spaces, known as depositing floors. Here, 

 exposed to frost, rain and sunshine, it gradually weathers, becoming friable and crumbling, 

 when it is fit to undergo the process of washing. The weathering of the material,' which is 

 accompanied by a change from the normal colour of " blue ground " to that of " yellow 

 ground," takes from one to nine months, according to the character of the weather to which 

 -it has been exposed, and to the mine from which the material was taken. " Blue ground " 

 from the Kimberley mine weathers in about half the time required for the same process by 

 the material from De Beer's luine; the latter sometimes requires several years for the 

 completion of the process, while a few months is usually all that is necessary for material 

 from the Kimberley mine. 



