A System of Instruction in the Practical Use of the Blowpipe | Page 8

fusibility of a substance. There is another point to which we would direct the student. Those metals which are volatile in the reduction flame, appear as oxides in the oxidation flame. These oxides make sublimates upon the charcoal close in the vicinity of the substance, or where it rested, and by their peculiar color indicate pretty correctly the species of minerals experimented upon.
(_b._) _Platinum Supports._--The metal platinum is infusible in the blowpipe flame, and is such a poor conductor of heat that a strip of it may be held close to that portion of it which is red hot without the least inconvenience to the fingers. It is necessary that the student should be cognizant of those substances which would not be appropriate to experiment upon if placed on platinum. Metals should not be treated upon platinum apparatus, nor should the easily reducible oxides, sulphides, nor chlorides, as these substances will combine with the platinum, and thus render it unfit for further use in analysis.
(_c._) _Platinum Wire._--As the color of the flame cannot be well discerned when the substance is supported upon charcoal, in consequence of the latter furnishing false colors, by its own reflection, to the substances under examination, we use platinum wire for that purpose, when we wish to examine those substances which give indications by the peculiar color which they impart to fluxes. The wire should be about as thick as No. 16 or 18 wire, or about 0.4 millimetre, and cut into pieces about from two and a half to three inches in length. The end of each piece is crooked. In order that these pieces should remain clear of dirt, and ready for use, they should be kept in a glass of water. To use them, we dip the wetted hooked end into the powdered flux (borax or microcosmic salt) some of which will adhere, when we fuse it in the flame of the blowpipe to a bead. This bead hanging in the hook, must be clear and colorless. Should there not adhere a sufficient quantity of the flux in the first trial to form a bead sufficiently large, the hook must be dipped a second time in the flux and again submitted to the blowpipe flame. To fix the substance to be examined to the bead, it is necessary, while the latter is hot, to dip it in the powdered substance. If the hook is cold, we moisten the powder a little, and then dip the hook into it, and then expose it to the oxidation flame, by keeping it exposed to a regular blast until the substance and the flux are fused together, and no further alteration is produced by the flame.
The platinum wire can be used except where reduction to the metallic state is required. Every reduction and oxidation experiment, if the results are to be known by the color of the fluxes, should be effected upon platinum wire. At the termination of the experiment or investigation, if it be one, to, clean the wire, place it in water, which will dissolve the bead.
(_d._) _Platinum Foil._--For the heating or fusing of a substance, whereby its reduction would be avoided, we use platinum foil as a support. This foil should be of the thickness of good writing paper, and from two and a half to three inches long, by about half an inch broad, and as even and smooth as possible. If it should become injured by long use, cut the injured end off, and if it should prove too short to be held with the fingers, a pair of forceps may be used to grasp it, or it may be placed on a piece of charcoal.
(_e._) _Platinum Spoon._--When we require to fuse substances with the acid sulphate of potash, or to oxidize them by detonation with nitrate of potash, whereby we wish to preserve the oxide produced, we generally use a little spoon of platinum, about from nine to fifteen millimetres[1] in diameter, and shaped as represented in Fig. 7. The handle of this spoon is likewise of platinum, and should fit into a piece of cork, or be held with the forceps.
[1] The French millimetre is about the twenty-fifth part of an English inch.
[Illustration: Fig. 7.]
(_f._) _Platinum Forceps or Tongs._--We frequently are necessitated to examine small splinters of metals or minerals directly in the blowpipe flame. These pieces of metallic substances are held with the forceps or tongs represented as in Fig. 8, where ac is formed of steel, and aa are platinum bars inserted between the steel plates. At bb are knobs which by pressure so separate the platinum bars aa, that any small substance can be inserted between them.
[Illustration: Fig. 8.]
(_g._) _Iron Spoons._--For a preliminary examination iron spoons are desirable. They may be made of sheet iron, about one-third