METALS AND CYANIDE PROCESSES 229 



All of the long used methods of securing the gold have 

 been open to criticism with regard to efficiency or economy. 

 Thus, in the working of placers or free milling ores, some- 

 times the finest particles of gold were not precipitated by 

 the riffle bars or caught on the blankets, but floated away 

 with the slimes; again, the grains of gold were often rusty, 

 or so coated as to refuse to amalgamate when brought in 

 contact with the mercury, and hence, in spite of the use of 

 metaUic sodium, or of potassium cyanide and other chemicals, 

 much gold escaped; or the presence of lead, copper, arsenic, 

 antimony, or other substances in the ore caused the mercury 

 to become foul, and therefore unable to take up gold. These, 

 combined with other causes of loss, have led to the estimate 

 that although gold to a value of over $1,000,000,000 has been 

 produced m California since 1848, yet more has been wasted 

 in milling and hydraulic mining by being washed down the 

 rivers and even to the ocean. 



Such were the conditions that existed in 1888, when, 

 by tests made on a large scale, it was demonstrated that 

 the cyanide process for the recovery of gold and silver from 

 low grade ores was of practical value and low cost, making 

 it possible to work profitably the large bodies of low grade 

 ore scattered over the earth, and the enormous piles of tailings 

 accumulated around both abandoned and active mines and 

 mills and being continually added to as minmg and milling 

 proceeded. 



According to Eissler, the fact that gold when in a fine 

 state of division was soluble in cyanide of potassium was 

 already known in the middle ages, when the gilding of metals 

 was carried out by jewelers and alchemists by the use of 

 gold in cyanide solutions. Unless potassium cyanide was 

 at that time made from prussic acid obtained from vegetable 

 sources, it is difficult to reconcfle this with the statements 

 made by Watts, by Roscoe and Schorlemmer, and other 

 authorities, that potassium ferrocyanide was discovered 

 by Macquer in 1752 and hydrogen cyanide by Scheele in 1782; 

 for these, particularly the former, are the present sources 

 of potassium cyanide. It has long been known, however, 

 that in the kernels of the bitter almond, peach, apricot, plum, 



