SCIENTIFIC.

Otago Witness, Issue 1812, 13 August 1886, Page 36

SCIENTIFIC.

THE USE OF THE BLOW PIPE

COPPER (Continued).

I stated in my last article that copper compounds when moistened with hydrochloric acid, colour the flame asure blue. This re action is characteristic of copper, and is obtained when only a trace is present — one part in a thousand giving a distinct blue. Another rough way of detecting copper ores is to scrape them over the flame ' of a spiritlamp, when they will colour the flama a bright green or blue. - But the beginner requires a more conclusive than the above, hence it will be necessary to treat the ores on the charcoal, as follows : — If copper is suspected the ore should be well powdered, and thoroughly roasted first in the oxidising and then in reducing flame. This removes any sulphur arsenic or other volatile material, and converts the copper into oxide, or into metalic scales. The roasted ore is now mixed with soda, and heated strongly in the reducing flame, when it will yield red malleable globules of copper — if iron is absent. These are usually black on the surface from a coating of oxide, but they become red on scraping or filing them. If iron be present, only a more or less greyish red bead, slightly magnetic, is obtained, It is for this reason I have put them into two groups. Of course, if metallic red beads are obtained, that will be decisive ; but in the case of ores containtaining iron, a learner cannot easily recognise the beads as as copper alloy. It will therefore be necessary to perform the following experiments which distinguish at once all copper ores whether containing iron or not.

At the end of a platinum wire make a small loop, as large as a capital O. This loop is heated and quickly dipped into a little crushed borax which is fused into a round transparent bead, and which we shall apeak of as the " borax bead." It has the property of dissolving metallic oxides and forming different coloured glasses, according to the metals used. In the case of copper, the borax bead in a pure oxidizing flame is a greenish blue when cold ; being green when hot. Iron slightly interferes with this reaction. In the reducing flame, the bead is red, or brownish red, and opaque ; the presence of iron does not interfere with this.

In making these experiments it is advisable to take only a trace of the roasted ore on the bead at a time, and if the colour is not distinct, then to add a little more until the blue colour of the bead is obtained. Too much would produce a black opaque bead.

I may state here that it is desirable to perform all the experiments described in these notes in daylight, as the colours cannot be detected with certainty by candle light.