From the first I was much struck with the exceedingly fine state of division in which the gold existed in the ore. After roasting and very carefully grinding down in an agate mortar, I have never been able to get any pieces of gold exceeding the one-thousandth of an inch in diameter, and the greater quantity is very much finer than this. Careful dissolving of the pyrites and gangue, so as to leave the gold intact, failed to find it in any larger diameter. As this was a very unusual experience in investigations on many other kinds of pyrites, I was led further into the matter. Ultimately, after a number of experiments, there was nothing left but to test for gold as a sulphide.
Taking 200 grammes of pyrites from a sample assaying 17 ounces fine gold per ton, grinding it finely, and; heating for some hours with a solution of sodium sulphide (Na2S2), on decomposing the filtrate and treating it for gold I got a result at the rate of 12 ounces gold per ton. This was repeated several times with the same result.
This sample came from the lode at the 140 ft. level, while samples from the higher levels where the ore is more oxidized, although carrying the gold in the same degree of fineness, do not give as high a percentage of auric sulphide.
It would appear that all the gold in the pyrites (and I have never found any apart from it) has originally taken its place there as a sulphide.
The sulphide is an analysis of a general sample of the ore:
| Silica | 13.940 | p.c. | ||||
| Alumina | 6.592 | " | ||||
| Lime | 0.9025 | " | ||||
| Sulphur | 16.584 | " | ||||
| Arsenic | 33.267 | " | ||||
| Iron | 27.720 | " | ||||
| Cobalt | 0.964 | " | ||||
| Per Ton. | ||||||
|---|---|---|---|---|---|---|
| Nickel | Traces. | |||||
| Gold | 5 ozs. | 3 dwts. | 8 grs. | |||
| Silver | 0 ozs. | 16 dwts. | 0 grs. | |||
| ——— | ||||||
| 99.969 | ||||||
Nambucca Head's Gold Mining Company, Deep Creek, N.S. Wales, Oct. 9, 1891.—Chemical News.
SOME MEANS OF PURIFYING WATER.
There are several methods extant for the purpose of purifying and softening water, and in the following brief account some of the chief features of these methods are summarized. The Slack and Brownlow apparatus we will deal with first. This purifier is one which is intended to remove the matter in suspension in the water to be treated by subsidence and not by filtration. The apparatus consists of a vertical iron tank or cylinder, inside which are a series of plates arranged in a spiral direction around a fixed center, and sloping at an angle of 45° on both sides outward. The water to be dealt with flows through a large inlet tube fixed to the bottom of the cylinder, rises to the top by passing spirally round the whole circumference, and depositing on the plates or shelves all solids and impurities at the outer edges of the plates. Mud cocks are placed to remove the solids deposited during the flow of the water upward to the outlet pipe, placed close to the top of the cylinder. One of these tanks, a square one, is at work purifying the Medlock water at Manchester, and on drawing samples of water from nearly every plate, that from the lower mud cock showed considerable deposit, which decreased in bulk until the top mud cock was reached, when the water was quite free from deposit. It is stated that one man would be sufficient to attend to 20 of these purifiers.