GOLD MINING IN COLOEADO. 553 



retorts are used, holding from 100 to 300 ounces of amalgam; though, in 

 some others, retorts of several thousand ounces capacity are employed. The 

 common retort is a conical pot of cast iron, 4 or 5 inches in diameter at 

 top and 6 or 7 inches deep. A lip or flange is formed around the mouth by 

 iron rings, that are shrunk on, the upper surface of which is smoothly ground 

 and fitting to a corresponding surface on the under side of the cover. The 

 latter is put on and secured by clamps and a screw. The top is provided 

 with a curved neck, to which is fitted a long pipe, which, being kept in cold 

 water, serves as a condenser for the vaporized quicksilver. When charged, 

 the retort is heated in a common forge fire, gently at first, and afterward 

 strongly. The bullion obtained is usually from one-fourth to one-third, or 

 rarely one-half, of the original quantity of amalgam, while the quicksilver, 

 after being condensed, is recovered for further use. This crude bullion is 

 worth from $15 to $18 per ounce in coin, sometimes little more or less, but, 

 on an average, $16 50. As all the gold-bearing ores contain some silver, 

 there is always a little of that metal present in the bullion, and in those ores 

 that contain an unusual proportion of silver the value of the ounce of crude 

 bullion is considerably reduced by its presence, as in the case of the Flack 

 and California ore, of which the retorted bullion seldom exceeds $13, in coin, 

 per ounce. In this form the retorted bullion is usually sold by the producers 

 to the bankers at Central City. It is forwarded thence to the Branch Mint 

 at Denver, or to other establishments, where it is melted and run into bars or 

 ingots. In this melting process a portion of the impurity contained in the 

 bullion, consisting of iron, unexpelled quicksilver, dirt, &c., is removed, and 

 the bar of metal produced is of somewhat higher value than the crude bullion. 

 The loss in melting, therefore, varies according to the care with which the 

 amalgam is cleaned before retorting. The value of the melted bar, per 

 ounce, is generally about $18, in coin. Having reached this form, the metal 

 is generally shipped to eastern markets, where it is subjected to further pro- 

 cesses of separation and refinement. 



The following tabular statement shows the percentage of loss in melting 

 the retorted bullion, produced from several different lodes; the fineness of 

 the bar obtained, the proportions of gold and silver present being expressed in 

 70 



