. The microscope and its revelations. ividual crystals;of this we have often an example ona large scale on a frosted window;but microscopic crystallisations some-times present the same curious phe-nomenon (fig. 814). Avanturine,lapis lazuli, crystallised silver, &, very good specimens ; whilst thin sections of granite, gabbro, and other crystalline rocks, also of•agate, aragonite. piedmontite, the , and other minerals, arevery beautiful objects for the polariscopo. The actual process of the formation of crystals may be watchedunder the microscope with the greatest facility, all
. The microscope and its revelations. ividual crystals;of this we have often an example ona large scale on a frosted window;but microscopic crystallisations some-times present the same curious phe-nomenon (fig. 814). Avanturine,lapis lazuli, crystallised silver, &, very good specimens ; whilst thin sections of granite, gabbro, and other crystalline rocks, also of•agate, aragonite. piedmontite, the , and other minerals, arevery beautiful objects for the polariscopo. The actual process of the formation of crystals may be watchedunder the microscope with the greatest facility, all that is necessarybeing to lay on a slip of glass, previously warmed, a saturated solu-tion of the substance, and to incline the stage in a slight degree, so thatthe drop shall be thicker at its lower than at its upper edge. will speedily begin at the upper edge, where the pro-portion of liquid to solid is most quickly reduced by evaporation, andAvill gradually extend downwards. If it should go on too slowly,. FJI;. 814.—Crystallised silver. 1 Physikalische K r ij st all a g rapine, Leipzig, 1895. - Grumlriss der physikalischen Erystallographie, Leipzig 1896. Microscopical Physiography of the Rock-maJcing Minerals, London, Glaisher on Snow-crystals in 1855, Quart. Journ. Micros/-. Sci. vol. iii. 1855,1>. 179. See also C. A. Hering, Krijst. Bd. xiv. 1888, p. 250. 1096 MICROCEYSTALLISATION, ETC. or should cease altogether, whilst a large proportion of the liquidstill remains, the slide may be again warmed, so as to re-dissolvethe part already solidified, after \drich the process will recom-mence with increased rapidity. This interesting spectacle maybe watched under any microscope, but the instrument speciallydesigned by O. Lehmann l is particularly adapted to studies of thiskind. The degree of heat can be varied at will. The phenomenabecome far more striking, however, when the crystals, as they comeinto being, are made to stand out brigh
Size: 1472px × 1698px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
