 | 1827 - 532 Seiten
...it is used to produce flat surfaces on rubies and other precious stones. It was also shown that tine drills are made of small splinters of bort, which are used for drilling small holes in rubies and other hard stones, for the use of watch-jewellers, .gold and silver wiredrawers,... | |
 | Andrew Ure - 1844 - 756 Seiten
...of polishing any gems ; but it is used to produce flat surfaces on rubies and other precioas stones. Fine drills are made of small splinters of bort, which are used for drilling small holes in rubies, and other hard stones, for the use of watch-jewellers, gold and silver wiredrawers,... | |
 | J.D. Dana - 1855 - 440 Seiten
...others. Those diamonds that are unfit for working, are sold for various purposes, under the name of tort. Fine drills are made of small splinters of bort, which...and but little loss of light, compared with similar lenses of other materials. They often have an irregularity of structure when perfectly pellucid, which... | |
 | Andrew Ure - 1860 - 786 Seiten
...of polishing any gems ; but it is used to produce flat surfaces on rubies and other precious stones. Fine drills are made of small splinters of bort, which are used for drilling small holes in rubies, and other hard stones, for the use of watch-jewellers, gold and silver wiredrawers,... | |
 | James Dwight Dana - 1876 - 458 Seiten
...employed for cutting glass; and for this purpose only the natural edges of crystals can be used, anc those with curved faces are much the best. Diamond...aberration, and consequently a larger field, and but little los* of light, compared with similar lenses of other materials. They often have an irregularity of... | |
 | James Dwight Dana - 1878 - 502 Seiten
...sold for various purposes, under the name of lort. Drills are made of small splinters of bort, and used for drilling other gems, and also for piercing...artificial teeth and vitreous substances generally ; and, others of iron set with a few diamonds, for drilling rocks. Graphite. — Plumbago. Hexagonal.... | |
 | James Dwight Dana - 1887 - 562 Seiten
...various kinds for jewellers, lapidaries, and others. Drills are made of small splinters of bort, and used for drilling other gems, and also for piercing...artificial teeth and vitreous substances generally; and others of iron set with a few diamonds, for drilling rocks. Graphite.—PI um bago. Hexagonal.... | |
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Fine drills are made of small splinters of bort, which are used for drilling other gems, and also for piercing holes in artificial teeth and vitreous substances generally. The diamond is also used for lenses for microscopes. When ground plano-convex,... 