70 JOURNAL OF THE 



separate portions, maintaining, however, the proportion between 

 them. 



After the gold has been converted into soluble chloride, which 

 generally happeus, as before stated, in 8 or 10 hours, the chlo- 

 rinator is discharged into the filter. 



The filters are wooden boxes 6 feet wide, 8 feet long, 1J feet 

 deep, lined with lead and filled for 6 in. to 7 in. with gravel, as 

 follows: A false bottom is laid, provided with numerous small 

 outlets; this false bottom was formerly made of wood, but is 

 now made of perforated tiles. On it is placed first a layer of 

 very coarse gravel about 1 in. in thickness, and so on up to the 

 height of 6 in. to 7 in., the material of each succeeding layer being- 

 smaller than that underneath, the topmost layer being fine sand. 

 Made in this way a filter will last from 12 to 18 months without 

 being renewed. The material discharged from the chlorinator 

 is a mixture of solid and liquid substances, the solids being oxide 

 of iron, gangue, sulphate of lime and silver chloride if any sil- 

 ver is present. The liquid being aqueous solution of the chlo- 

 rides of gold, copper and iron with some free sulphuric acid, the 

 filter retains the solids, while the liquids drain away in suita- 

 ble vats. The filter is washed until all the gold chloride is 

 washed out, which is ascertained by observing whether the 

 last filtrate reacts with copperas solution. Time required for 

 filtering and washing a charge is from two to three hours, 

 and amount of wash-water used is about three hundred gallons; 

 the leached ore on filter is thrown away, unless by panning 

 it is found that the free gold has not been dissolved; .in this 

 case it is re-chlorinated, if the amount is sufficient to warrant 

 the expense. If much silver be present, it will be on the filter 

 as chloride and can then be leached out with " hypo," and pre- 

 cipitated with hydrogen sulphide. The gold solution is stored 

 in lead-lined wooden tanks holding about 1,800 gallons. A 

 sufficient quantity is from time to time run into precipitating 

 vats lined with lead and then precipitated as metallic gold 

 by ferrous sulphate. Thrown down in this way gold is a very 

 fine brownish powder and requires about four days to settle. 



