4 86 SCIENCE PROGRESS. 



was only the introduction or adaptation of a process already 

 well known in Europe. 



The existing methods of washing auriferous sands all 

 depend on two principles, the great density of gold when 

 compared with that of the siliceous material with which it 

 is associated, and, as Baron Born expressed it over ioo 

 years ago, the " elective affinity" of mercury for gold when 

 mixed with impurities. The ease with which gold-amalgam 

 can be collected in spite of its being less dense than gold is 

 of course due to the fact that it is miscible in all proportions 

 with mercury, so that under proper conditions large 

 globules of liquid alloy are formed by the running-to- 

 gether of smaller particles, and the former are readily 

 caught in suitable crevices. 



A large number of implements of varied form and 

 efficiency are used in different parts of the world to apply 

 these principles. In operations on a small scale the batea, 

 the trough, and the miner's pan are chiefly used. In South 

 America, in West Africa, and in parts of China, the batea is 

 used, a wooden vessel having the shape of a very short 

 reversed cone. When held in the hands and filled with 

 gravel and water, a peculiar gyratory motion imparted to it 

 results in the collection of the gold in the apex of the 

 cone, and the light material can then be readily washed 

 away. 



A small wooden trough, twelve or fifteen inches long, is 

 used for the same purpose in the far East by the Chinese, 

 the Tonquins, the Annamites, the Malays, and others, the 

 water being made to flow up and down until the gold has 

 settled to the bottom. The miner's pan, a flat-bottomed 

 iron vessel with sloping sides, was first used by the 

 Californian pioneers, but has now become the favourite 

 implement of Europeans for prospecting in all parts of the 

 world. In early days in Australia and California millions 

 of ounces of gold were obtained from the river gravels 

 by its use, but apart from its value in prospecting it is 

 at most a rough and ready means of treating small 

 quantities of rich material, and is only suitable to individual 

 effort. 



