TESTING MINERALS.

Inangahua Times, Volume VII, Issue 1046, 8 February 1882, Page 2

TESTING MINERALS.

» For the all-important purpose of seeing with certainty whether in making a discovery of a mineral, it is one or other of the more valuable varieties dealt with in this treatise, no great preparations are necessary. The ordinary tests applied, in addition to what may be seen by comparison with other minerals, are to prove its weight or specific gravity hardness, fusibility, &c. In order to get these particulary the blowpipe, a pair of small scales, a candle, carbonate are necessary. Five shillings may provide all the plant actually requisite. If a magnet is added so much the better. After some practice the eye, by judgment of the colour and form, is a great aid in arriving quickly at a correct conclusion. The Blowpipe. — Direction for the use of this little machine can be got in any chemical work ; what has to be said of it here will be very brief. To use it the breathing must be all through the nostrils and after a brief practice a steady flow of air can be maintained — sufficient at all events, to fuse many valuable minerals. A common candle answers all the necessary purpose to get up the requisite heat by the aid of the blowpipe blast. It is a real heat manufactory, and intense heat is engendered. The blast from the blowpipe should be directed steadily into the flame of the candle, the wick being first bent down a little, and the blast of air from the nozzle of the pipe passing slightly over the wick. The main heat for testing is got just beyond the point of the flame. This is the deoxidizing or reducing part of the flame. The three usual means of testing minerals before the blowpipe are — with borax; on charcoal, usually with the addition of soda ; by holding in the oxidizing point These agents and a bit of platinum wire are necessary for experimenting. Making an Experiment. — In the first place the mineral to be tested should be pounded as fine as possible. Then bend the platinum wire until a small ring or loop about the twelfth part of an inch is obtained. Put the hoop in the candle flame before the blowpipe, and when white hot dip it into borax. The particles of the latter which adhere to the wire are next fused in the flame, and the operation is repeated and repeated until the small loop or ring contains a bright bead of fused borax. This bead is then applied to the pounded mineral, and again submitted to the flame. If no colour is imparted a fresh trial has to be made, for in this experiment the test is one of color. When properly carried out the following may result if the metals are present : — Colour of Bead in : Oxidizing. Reducing. Metal present. Green (hot,) Red Copper blue (cold) Bottle green Iron Red or yellow Grey and Nickle (hot) turbic Viclet (hot) Charcoal and Blowpipe Test. — Get a bit of charcoal (that of stringy-bark without flaws or cracks does very well ; scoop out a small hollow, the size of a pea, and fill it with the pounded mineral, mixed with more than equal bulk of carbonate of soda. Bring the blowpipe flame to hoar on it gently and when fused n little let it have full force of the heat. Tf tin is being tried for add a little bit. of cyini-lo r>F •pof" n ':>' i nm "V«*}mn .•'-.'-••' • I •.,...■ . . ..■"!.

charcoal, the test is complete. The nature of the metal is judged by the following appearance : — ' Colour of Globule. Metal present. Yellow and malleable ... Gold White " Silver Red " Copper White, bright " Tin White " Lead White, brittle " Bismuth ' White, brittle, giving off fumes when 1 removed Antimony : Acid fob Testing. — Nitric acid can be employed with good effect To use it, pound the mineral fine, as in the former case, then take a small portion, and saturating it with the acid, lay the mixture on the blade of a pen-knife, which should be polished bright. Or the mixture of mineral in acid can be boiled over a candle in a test tube. Particles of the mineral will be deposited on the knife or in tuba Specific Gravity Test. — The weight of a mineral aids materially in its identification. The rule to be observed in the case is to weigh a portion of the mineral carefully, and tying it to a thread, fasten the thread to a balance or scale, and immerse the* mineral carefully in water. The difference in tiie weight of the specimen as it hung in the air, and the same in the water, gives the specific gravity test Example : — A piece of quartz weighing 1398 grains in the air and 862 grains in water, shows a difference of 536 grains. The rule is to divide by 2.6, which is the specific gravity of quartz.