Manual of qualitative analysis / by Robert Galloway.

  • Galloway, Robert.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: Manual of qualitative analysis / by Robert Galloway. Source: Wellcome Collection.

    253/272 (page 235)
    If the loop of the platinum wire when moistened is slightly brought into contact with the powder or the grain of the substance to be examined, it adheres to it, and when some time warmed near the flame, and then introduced into it, the substance melts and fuses into a drop or bead. Spluttering substances must first of all be brought to a red heat in a covered platinum spoon. By means of the holder fig. 3, the substance under examination can thus be brought to any part of the flame required. The temperature of the flame depends mostly on the composition of the gas; it will be found that the hottest part of the flame is in a zone of the external mantle adae, which extends a few millimetres above and below the diameter of the flame at 6. This region, which may be called the melting-space, is used to determine the deport- ment of bodies at the temperature of 2300° C. The external edge of this melting-space acts as an ovidising flame, and the internal as a reducing flame. The latter is most powerful just below the point 0. The great constancy of the flame permits it to be used for determining the volatility of bodies at 2300° C. This is effected by melting on the platinum wire as much of the substance to be tested as will form, when seen under the microscope, a bead of 1 millimetre in diameter: with a little practice this is very easy. After the bead has been brought to the right size, and warmed by being brought near the flame, it can, by a very slight movement of the arms of the holder (fig. 8), be introduced into the melting-space of the flame, and the seconds which elapse until it has quite evapo- rated are counted by means of a pendulum or metronome. This point is generally so marked by a sudden alteration of the flame as to be determinable to half a second. Taking the volatility of carbonate of soda as unity, we