Hydrostatic Balance

From The Gemology Project
Revision as of 05:35, 7 October 2006 by Doos (talk | contribs)
Jump to: navigation, search
Exlamation mark.jpg
This section is currently under construction, do not edit until this message is gone
--Doos 12:34, 6 October 2006 (PDT)

The hydrostatic balance is used to determine the specific gravity of a gemstone. Although it is a fairly simple apparatus to operate it can be time consuming and one would need to put the results in a calculation, something not all gemmologists enjoy doing.

Basic

Specific gravity (SG) is a constant ratio of an object compared to water. When an object in totally immersed in water it will experience an upward trust that is equal to the volume of water which is displaced by the object. This will make the object appear lighter in water.
The first to observe this was Archimedes while investigating a possible fraud with the crown King Hiero of Syracuse (present day Sicili).

Archimedes and Archimedes' Law

When King Hiero commisioned a new gold crown a certain volume of gold was provided to a goldsmith, who manufactured the crown to the liking of the king. Soon after rumours started that the goldsmith may have been frauduleus and added silver to the gold, making a nice profit for himself on the side.
King Hiero asked Archimedes to investigate and one day while taking a bath, Archimedes noticed that his body mass caused the water in the bath to overflow. In his excitement over finding a possible answer to the problem he ran home naked, shouting "eureka" (I found it).

He immersed equal volumes of gold and silver in water and by observing the amount of water that was displaced, he noticed that the mass of gold displaced less water than the silver. He then immersed the crown and through a series of calculations he was able to determine how much gold and silver was used to create the crown. The fraud was detected and this was the first time in history SG was used.

Archimedes Law (or the Law of Buoyancy) states that: the upward force on an immersed object is equal to the weight of the displaced fluid.

In gemmology 3 different types of hydrostatic balances are used.

  • The two-pan scales
  • The one-pan scales
  • Spring balances

Two-pan scales

Hydrostatic2.png
Hydrostatic.png


External links