Fusion by Means of Blowpipe Flame

A good blowpipe flame may reach a temperature as high as 2000º C. When skillfully handled small pieces of fine platinum wire may be melted in it. The determination of the degree of fusibility of a mineral is an Important aid to its identification. In order to make the test, a small and if possible a sharply pointed fragment of the mineral should be inserted into the blowpipe flame just beyond the tip of the inner cone, where the combustion is most rapid and the temperature the highest. The fragment should be held as illustrated which it is hell in such a manner that the entire heat of the flame can be concentrated upon it. If it melts and rounds over, losing its sharp outline, it is said to be fusible in the blowpipe flame.

Minerals can therefore be divided into two classes, as to whether the are fusible or infusible in this flame. The minerals which are fusible can be further classified according to the degree of ease with which they fuse. To assist in this classification, a series of six minerals which show different degrees of fusibility has been chosen as a scale to which all fusible minerals may be approximately referred. For instance, when a mineral is said to have a fusibility of 3, it means that it will fuse with the same degree of ease as the mineral which is listed as 3 in the scale. In makings such comparative tests, it is necessary to use fragments of the same size and to have the conditions of the experiments uniform. The minerals of the scale of fusibility are as follows:

1. Stibnite. Very easily fusible. A small splinter will readily melt in a candle flame.
2. Chalcopyrite. Easily fusible. A small fragment will fuse in the Bunsen burner flame.
3. Almandine Garnet. Infusible in the Bunsen burner flame but fuses easily in the blowpipe flame.
4. Actinolite. A sharp-pointed splinter fuses without much difficulty in the blowpipe flame.
5. Orthoclase. The edges of a fragment are rounded at the highest head of the blowpipe flame.
6. Enstatite. Practically infusible in blowpipe flame, only the fine ends of sharp-pointed fragments being rounded.

Reducing and Oxidizing Flames. Reduction consists essentially in taking oxygen away from a chemical compound, and oxidation consists in adding oxygen to it. These two apposite chemical reactions can be accomplished by means of a blowpipe flame. Cone b, Fig. 202, as explained above, contains CO, or carbon monoxide. This is whats is wowing as a reducing agent, since, because of its strong tendency to take up oxygen away From another substance in contact with it. For instance, if a small fragment of the ferric oxide o f iron, hematite, Fe₂O₃, is held in this part of the blowpipe flame, it will be reduced by the removal of one atom of oxygen to the ferr4ous oxide, FeO, according to the following equation:

Fe₂O₃ + CO = 2FeO + CO₂.

This change can be proved by noting that the ferric oxide is red in color and nonmagnetic, while the ferrous oxide is black and strongly magnetic. This cone b is therefore known as the reducing part of the blowpipe flame, and when it is wished to perform a reduction test the mineral fragment is placed at r.

On the other hand, if oxidation is to be accomplished, the mineral must be placed entirely outside of the flame, where the oxygen of the air can have free access to it, but where it can still get in large degree the heat of the flame. Under these conditions, if the reaction is possible, oxygen will be added to the mineral and the substance will be oxidized. The oxidizing part of the blowpipe flame is at a (Fig. 202). Pyrite, FeS₂, for instance, if placed in the oxidizing flame, would be converted into ferric oxide, Fe₂O₃, and sulfur dioxide, SO₂, according to the following equation:

2FeS₂ + 110 = Fe₂O₃ + 4SO₂.

The ferric oxide would form a dark-red residue, while the sulfur dioxide would come off as a pungent-smelling gas.

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