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Gem-Stones and Their Distinctive Characters

Chapter 129: FOOTNOTES:
By George Frederick Herbert Smith
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About This Book

A practical handbook describing the physical characters and identification methods for gemstones, combining clear accounts of crystalline form, optical properties (reflection, refraction, dispersion, double refraction), colour and absorption effects, specific gravity, hardness and electrical behaviour with practical techniques such as refractometer use and heavy-liquid tests. It outlines cutting, weighting and nomenclature, distinguishes manufactured and imitation stones, and provides species-by-species descriptions of precious and semi-precious gems — including diamond, corundum, beryl, topaz, spinel, garnet, tourmaline, zircon, quartz and chrysoberyl — accompanied by diagrams, plates and tables of physical constants for practical reference.

Printed by Morrison & Gibb Limited, Edinburgh

FOOTNOTES:

[1] The word medium is employed by physicists to express any substance through which light passes, and includes solids such as glass, liquids such as water, and gases such as air; the nature of the substance is not postulated.
[2] Methylene iodide must be heated almost to boiling-point to enable it to absorb sufficient sulphur; but caution must be exercised in the operation to prevent the liquid boiling over and catching fire, the resulting fumes being far from pleasant. It is advisable to verify by actual observation that the liquid is refractive enough not to show any shadow-edge in the field of view of the refractometer.
[3] γωνία, angle; μέτρον, measure. For details of the construction, adjustment, and use of this instrument the reader should refer to textbooks of mineralogy or crystallography.
[4] A cleavage flake of topaz may conveniently be used to show the phenomenon, but owing to the great width of the angle the “eyes” are invisible.
[5] In accordance with the usual custom the angle between the facets is taken as that between their normals, or the supplement of the salient angle.
[6] The word paste is derived from the Italian, pasta, food, being suggested by the soft plastic nature of the material used to imitate gems.
[7] Cf. below, p. 149.
[8] The least and the greatest of the refractive indices of doubly refractive species are given.
[9] The dispersion is the difference of the refractive indices corresponding to the B and G lines of the solar spectrum. The value for crown-glass is ·016.
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Transcriber’s Notes:
  • Redundant title page has been removed.
  • Blank pages have been removed.
  • Front publication list moved to the back.
  • Silently corrected typographical errors.
  • Where possible Unicode fractions have been used, otherwise they are formatted using superscript/subscript, which appears somewhat different.