PLAIN DIRECTIONS FOR TESTING MINERALS.—Continued.

Waikato Times, Volume I, Issue 27, 2 July 1872, Page 2

PLAIN DIRECTIONS FOR TESTING MlNEßALS.—Continued.

3. The Blowpipe and its Appliances. The operator having made himself acquainted with the above preliminaries, may proceed to the use of what ih tasting minerals is by far the most important and useful instrument —the blowpipe. A great deal can be learnt respecting minerals, by a few; simple trials with the blowpipe. The only requirements are a common blowpipe, a candle, a forceps or pliers, a bit of charcoal, a piece of No. 7 platinum wire, two inches long, dried carbonate of soda, dried borax, and cyanide of potassium. The bit of charcoal selected for these experiments should be free from cracks and openings. By dry carbonate of soda is meant not'merely dry to the touch, but quite free from water; this may be prepared from com mon washing soda, by expelling the water it contains. The washing soda is put in a shallow clean iron dish and placed over a clear fire until a white dry powder is formed ; too strong a heat might fuse the dry powder. A quarter of an ounce may be kept in a wellcorked bottle or tube for use. Bicarbonate of soda may be used instead withe ui previous heating ; or if the bicarbonate of soda be moderately heated, it looses weight, and becomes carbonate of soda, quite free from water, like the above. The borax is to be dried in the same way ; a quarter of an ounce will be enough) it is convenient to keep the platinum wire in the same tube. Unless these tubes are well corked these chemicals re-absorb moisture. For testing tin ore it is useful to have a little cyanide of potassium, kept in a bottle with the cork and rim well covered with beeswax ; it would otherwise liquefy, by absorption of moisture, and becomo useless. It is a most dangerous poison, and the greatest caution must be observed in its use. 4.— Use of the Blowpipe. Some practice is required before the blowpipe can be used with certainty. The instrument should have a fine aperture, merely large enough to admit a fine needle. The beginner may readily acquire the mode of using it by first breathing through the nostrils, with the lips closed, then puffing out the cheeks (as if rinsing the mouth with water), still keeping the lips closed and breathing as before; the blowpipe may at this point be slipped between the lips, and it will be found that a current of air escapes through it without any effort on the part of the operator. Air flows through the pipe owing to the tendency of the distended cheeks to collapse; it must never be forced ; from the lungs. After a little practice, the '

strength of tho current may be increased. By breathing entirely through tho nostrils, Japping the lips closed tho blast may be kept up for ten minutesor longer withoutexhaustion or inconvenience, except a slight fatigue of tho lips in holding the blowpipe. Tho flame of a common candle is one of the host to employ. Three kinds of effect can bo produced by the blowpipe. First—lt can be used as a source of heat for testing fusibility; for this purpose it :s well to know where to find the hottest part of the flame. Secondly—lb can add oxygen to mineral. Thirdly—lt can take oxygen away. A knowledge of tho structure of a candle-flame will facilitate tho attainment of these objects. A candle may be considered a gas manufactory on a small scale ; once alight, tho heat melts the wax, which ascends the wick, and finally becomos gas ; the hot gas and tho oxygon of the air combine togethor, or, as wo say, burn. The dark, inner part of a candleflame is where the gas is distillod from tho wick : at tho high temperaturo of tho flamo this combustible gas oombinos readily with oxygen gas ; and it has also the power o depriving many solid substances of oxygen. As the combustible gas spreads outwards from the central dark space, it meets with oxygen gas in the air, and its combustion becomes mora and more perfect on approaching the surface. The luminous part is where the combustion is still imperfect. If a substance bo held just above the apex of a flame, ! the current of air, mechanically carriod along by tho flame, strikes upon it, and under theso circumstances many substances absorb oxygen gas. If air is blown upon a flame, the supply of oxygen is increased, the burning becomes more complete, and the heat is intensified. If, with the blowpipe, a steady current of air bo directed horizontally through the flamo, placing the jet within the flame's border, a little above the wick, which may be slightly bent down, two sharply defined conea of flamo w ill be thus produced; an inner blue cone, aud an outer feebly luminous one.

The tip of the blue cone is the hottest part of the flame, and it is hero that a fragment of a mineral should be held in testing its fusibility. To add oxygen, or, as it is often termed, to oxidize or roast a mineral, it should be held at the very tip of the outer flame, where it may be kept in a strongly heated state, and allowed to absorb oxygen from the surroundiug air to the extent of its power. Only a small portion of the blowpipe flame is suitable for the third purpose, —to removo oxygen, or deoxidize, or reduce. A mineral may be deprived of oxygen (reduced), by the combustible gas of the candle, but the only part of the blowpipe flame whero Ihis gas exists in an available form is in the outer cone, just in front of the inner blue cone. The mineral to be deoxidized must be completely enveloped in this burning gas, for, if it projects beyond the flame, it absorbs oxygen from the air as fast as the combustible gas removes it. For deoxidizing, or reducing, it is convenient to increase the size of the suitable part of the flame by blowing in a different manner. This may be done by removing the jet out of the flame, keeping it slightly above the level of the bent-down wick, and blowing gently so as to make the flame roar slightly, but without destroying its entire luminosity. The interior of this flame near its extremity will ba found to possess strong reducing power. The three principal means of chemically testing minerals before the blowpipe are, (1) with borax; (2) on charcoal, usually with tho addition of carbonate of soda; (3) by holding in the oxidizing point.