If the substance dissolves in the microcosmic salt slowly and only in small quantity, the bead being colourless and remaining so after cooling, the undissolved portion looking semi-transparent, and if upon the addition of a little sesquioxide of iron it acquires the characteristic colour of an iron bead—this denotes SILICIC ACID.
For producing extreme degrees of heat the flame is blown with a jet of oxygen gas, the instrument being then called an OXYGEN BLOWPIPE; or a mixture of oxygen and hydrogen is burned, when it is called an OXY-HYDROGEN BLOWPIPE. The heat produced by the last is so great that no substance can stand exposure to it, even the most refractory native compounds being immediately fused. Gold is volatilised, and iron is rapidly consumed the instant it is placed in the flame.
1. Hemming’s safety-jet for the oxy-hydrogen blowpipe.
a, Pipe conveying oxygen gas.
b, ” hydrogen gas.
c, Ball stuffed with fine wire-gauze.
e, Jet (internal diameter 1-80th of an inch).
2. Black’s blowpipe.
3. Bergman’s blowpipe.
4. Pepy’s blowpipe.
5. Wollaston’s blowpipe.
6. Oxy-hydrogen blowpipe.
The principal varieties of the blowpipe in
general use are figured in the engravings above.
Beside the above there are several other varieties of the blowpipe occasionally employed; one in which the air is expelled by the pressure of a column of water, and hence called the HYDROSTATIC BLOWPIPE; another, in which the flame is blown with the vapour of boiling alcohol, is named the SPIRIT-BLOWPIPE.
Blowpipe, Herapath. For sealing and bending glass tubes and constructing glass apparatus of various forms, it is convenient to have the blowpipe mounted on a fixed support, and when a flame of considerable power is required, the blast must be supplied by bellows worked with the foot. A very convenient form of blowpipe for these purposes is that invented by Herapath, and represented in the following figure, a is a flexible tube attached to a stop-cock (b), which communicates with a tube (c d), bent at right angles at d, where a T-shaped tube (e f g) slips on by means of the piece f. The blow-pipe jet (h i) passes into the longer arm of the T-piece, and fits somewhat tightly; k l is a second piece of flexible tube, terminating in a mouthpiece, or connected with a blowing apparatus. On turning on the gas, it passes in the direction marked by the arrows, and is to be inflamed at e. On blowing with the mouth, or by means of a pair of bellows, into the tube k l, the ignited gas takes the form of a blow-pipe flame of great power, the nature of which is entirely under control by means of the stop-cock b, and also by regulating the quantity of air supplied through the tube (k l). The T-shaped piece is movable at f, so that the jet may be directed to any position. The apparatus may be mounted on a heavy foot, and connected with the gas-supply, by means of the flexible tube, so that it can be placed in any required position on the laboratory table; or it may be permanently fixed on a table specially devoted to the purpose, and having beneath it a pair of bellows worked by a treadle.
A simple and inexpensive apparatus for supplying a continuous blast of air for blowpipe or other purpose is figured below.