38 lEON PTEITES. 



mineral lying upon tlie hearth immediately above that removed is 

 brought into its place ; again, that still further up is brought a 

 stage lower, until the whole has been shifted, when the vacant 

 place at the upper part is refilled from the hopper. The sul- 

 phurous and arsenical vapours, together with the products of 

 combustion and dust from the pyrites, pass into a tunnel between 

 200 and 300 feet long, 4 feet high, and 3 feet wide, carried up 

 the side of a hill, terminating in a chimney 30 feet high. Nearly 

 all the sand and dust carried over by the draught is deposited 

 within 40 feet of the furnace, and is periodically removed for 

 retreatment, as it contains a notable quantity of gold ; beyond 

 40 feet the sand is worthless. From the size of the tunnel the 

 vapours move slowly onwards, and have, consequently, time to 

 deposit any heavy particles ; continuing their course, the vapours 

 passthrough six cellular brick screens, down which apowerful spray 

 of water passes ; here they get cooled and scrubbed, the sulphurous 

 and sulphuric acids dissolved out, whilst the arsenious acid is 

 deposited on the floor of the tunnel, scarcely anything escaping 

 from the chimney but the fuel vapours. Some alarm was felt by 

 the Town Council lest any arsenical vapours should escape and 

 prove injurious to the inhabitants, as the works were close upon 

 the township, and they placed the matter in the hands of Mr. 

 Johnson, the Grovernment analytical chemist, for investigation, 

 who reported as follows : — " I drew five gallons of the vapours from 

 the chimney of the roasting furnace, and by the application of 

 one of the most delicate tests known to science, viz., Eeinck's 

 test, discovered but the merest trace of arsenic." I may remark 

 that when this investigation took place we were condensing over 

 two tons of arsenic per month in the tunnel. I have dwelt 

 somewhat lengthily upon this part of my subject, as I am desirous 

 to show that with due precautions such operations can be safely 

 carried on ia the neighbourhood of habitations. 



In carrying out the roasting operations the work is divided 

 into three shifts of eight hours each, one man being able to 

 attend a furnace ; his business being to keep up the fire, charge 

 and discharge the furnace, and finally to cover up the hot sand 

 discharged with damp sand and spray it with water. This 

 quenching was found to be a matter of some importance, as the 

 quartz sand — always found with the pyrites — is thereby broken 

 up and rendered friable, by which the after-process of grinding 

 is greatly facilitated. The quantity of sand which a furnace of 

 the above-mentioned size can treat will average 4 tons per 

 twenty-four hours, with a consumption of 3-lOths of a cord 

 of wood per ton. 



Having determined upon a mechanical process for extracting 

 the gold from the roasted mineral, it became necessary to dis- 

 cover the best condition for accomplishing it. In this also we 



