lEON PTEITES. 37 



Here it will be observed tliat, with the raw sand, only a small 

 proportion of the gold was obtained — a very much larger was 

 left in the tailings, although finely ground ; and a large j: ro- 

 portion was carried off with the water as slime. With the 

 roasted mineral more than half the gold was obtained ; the 

 tailings were much poorer than those from the raw sand, but 

 still very rich, and a large quantity was carried off by the water. 

 After carefully considering the merits of the various methods 

 suggested for extracting gold from pyrites, it was determined to 

 attempt it by a mechanical process. Profiting by our acquired 

 knowledge of the condition of gold in pyrites, our first 

 problem to solve was how to best destroy the enveloping 

 sulphides and arsenides, so as to get rid of the deleterious action 

 of those minerals upon the mercury used for amalgamating and 

 detaining the liberated gold ; and, secondly, the best method of 

 extracting the gold from the decomposed pyrites. After a num- 

 ber of experiments on a large scale, it was decided to effect the 

 decomposition of the pyrites by a roasting process. To effect 

 this economically, I devised, and in conjunction with Mr. H. A. 

 Thompson patented, in 1862, the Inclined Eoasting Furnace, 

 which is now used in many places throughout the Colonies. It 

 consists of an inclined roasting hearth, usually about 30 feet 

 long by 5 feet wide ; the fire-hole for heating the hearth crosses 

 the lower end of it, and is separated from it by the fire-bridge ; 

 between the latter and the hearth is a channel for carrying into 

 the store-pit the sand when roasted. In the foot wall of the 

 furnace are six tubes, from 1| to 2 inches diameter, for supplying 

 heated air to the roasting sulphides ; scarcely any air is admitted 

 through the fire-bars, the gaseous vapours from the fuel being 

 completely burned by the great excess of air passing over the fire 

 for oxidising the pyrites. Along each side of the furnace are 

 five working doors, for the workmen to turn and rake down the 

 mineral. Above the upper end of the furnace a large hopper is 

 constructed capable of holding twenty-four hours' supply of 

 sand ; in the floor of this hopper is a trap for supplying mineral 

 to the hearth ; the hopper is filled by trucks, communicating 

 with the buddies by a tramway to the stamp-house. The whole 

 of the furnace is carefully braced with vertical, longitudinal, and 

 transverse ties. The present furnace has been working about 

 ten years, and, with fair treatment, will last many years more. 

 In working this furnace the whole of the hearth is covered with 

 pyrites to a depth of between two and three inches, kept at a 

 gentle red heat, with frequent stirring, until the mineral nearest 

 the fire, and about six feet beyond it, is found no longer to give 

 off sulphur fumes. An experienced workman can determine 

 when this condition has been attained by it appearance in the 

 furnace. It is then raked into the discharge-channel, and the 



