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Ch. 2: Gems in Ceylon

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GOLD IN INDIA.
157
after another has been tried, and it has been found in this as in all other appliances for treating auriferous pyrites and auriferous quartz, that the simplest plan is invariably the most efficacious. An inclined reverberatory furnace on the following plan is highly approved of in Australia:—It consists of a fire-box from which the heat and products of combustion pass over a hearth into con­densing chambers. The charge is supplied through a hopper and gradually drawn down over the hearth by rakes until it reaches a channel near the fire-box, whence it is drawn into a pit at the side of the furnace. Four or five small doors are provided into which the rakes are inserted. As the charge is drawn downwards to the bottom of the hearth it becomes gradually heated more and more, and to such a degree as to decompose the sulphides. The roof of the furnace over the hearth should be arched.* In a well-constructed reverberatory (oxidating) furnace all the sulphides thrown into the bed are completely decomposed in a short time.
A dull red heat is maintained throughout, and until the sand is actually raked out into the pit, there is a continuous stream of heated air playing upon the pyritous minerals.
Metlwds of testing aurijerous quartz and auriferous pyrites.-.-Only by a careful chemical analysis can the proportion of gold in any given quantity of quartz, pyrites, or other mineral be ascertained; but for all practical purposes, assays by amalgamation are sufficient. The methods pursued in treating quartz taken from the reefs in the Wynaad have been as follows:—
When a reef was tested in sections, the stone from each section was taken out in far larger quantities than were required for testing; each heap of quartz was broken into small pieces, and the whole was well mixed, and from the heap so mixed the portion to be treated was taken. The stone was broken still smaller and weighed, and it was then ground very fine on a suitable stone, another stone being used as a muller. The finely pulverised stone was put into a clean iron pan and roasted until fumes were no longer given off until it was certain that it was in a lit state for amalgamation. If after roasting the pulverised material seemed to require it, it was again ground on the stone. The heat at all times was so regulated as to prevent the possibility of " glazing."
The roasted stone was put into an enamelled dish, and a proper proportion of quicksilver was added.
The whole was then thoroughly rubbed by hand, at first dry; subsequently a little cold or hot water was poured in until a paste was formed; more water was added, the stuff being thoroughly rubbed all the time, and finally the amalgam or (if there was no gold) the quicksilver was washed off, the utmost care being taken to prevent the loss of any quicksilver. The water and sludge from the enamelled dish were poured into other vessels and these were most carefully examined subsequently, and if there was doubt,—and sometimes when there was no doubt as to the results, the s,ludge-sand, &c, in these were treated again,— the amalgam or quicksilver was most often placqd under the flame of the blowpipe, but at other times nitric acid was used and the gold (if any and of sufficient quantity) was weighed.
The results were calculated in the ordinary way,
It happened occasionally that the roasting was not sufficiently protracted, or that all the material subjected to the roasting was not ground as fine as it ought to have been, and then it became necessary to subject it to further roasting, or to use acids to decompose the sulphides. In all cases the utmost care was taken to preserve the conditions necessary for effective amalgamation.
The quartz collected in various localities was treated in the same manner as that taken from sections of the reefs.
In order the better to illustrate the value of this system of testing quartz, \ took a quantity of sludge and sand from which the gold had been extracted, and which had been saved in pans, and into this I put half a grain of very
Ch. 2: Gems in Ceylon Page of 442 Ch. 2: Gems in Ceylon
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