Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . is posi-tively electrified and is caught by the negative poles colonng themred. The dust should- fall evenly and the bellows be held farenough away to prevent direct action of the blast. *Poggendorf s Annalen, CLVIII., i, 425, 1876. f If heating injures the crystal it may be cooled from room temperature by a freezingmixture. J With rising temperature these are reversed. \ Dry over H^SO^ in a vessel from which the air has been partially exhausted. 186 DESCRIPTIVE MINERALOGY. Figs. 372, 373 and 374 sho
Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . is posi-tively electrified and is caught by the negative poles colonng themred. The dust should- fall evenly and the bellows be held farenough away to prevent direct action of the blast. *Poggendorf s Annalen, CLVIII., i, 425, 1876. f If heating injures the crystal it may be cooled from room temperature by a freezingmixture. J With rising temperature these are reversed. \ Dry over H^SO^ in a vessel from which the air has been partially exhausted. 186 DESCRIPTIVE MINERALOGY. Figs. 372, 373 and 374 show crystal of tourmaline, calamineand boracite respectively, the darker dotted portions represent-ing the accumulation of minium at the analogue poles and thehatched portions the accumulations of sulphur at the antiloguepoles. If the crystals had been dusted during the heating, the analoguepoles would have been coated with sulphur and the antilogue poleswith minium. In Piezoelectricity the charges are developed by pressure, forinstance, calcite pressed between the fingers becomes positively. Fig. 373. Fig. 374.
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