Three Weight Systems
This is a handy guide, cribbed from the web, containing
information on the weighing of GOLD,
Precious Metals and Gemstones.
A short history and explanation of the principal weight systems follows:
IMPERIAL
The IMPERIAL Weight system consists of 3 principal Measures: AVOIRDUPOIS,
APOTHECARIES and TROY.
Prior to the Industrial Revolution in England, the British Imperial standards
were evolved from the Greek,
Roman and French systems over many centuries.
With the spread of the British Empire around the globe, over the last few
hundred years,
the Imperial system reigned supreme, until fairly recent times.
In 1855, the British Parliament legalized the main measures of the Imperial
system.
Their arch rivals, the French, led by Napoleon Bonaparte were not to be outdone,
and it is they,
even though they had to bide their time, who eventually came out winners, with
the relentless march
of Metrication around the world.
Besides not being a decimal system, the other main factor in the downfall of the
IMPERIAL system
was its non-standardisation in various countries.
For instance, prior to 1958 the IMPERIAL INCH measured 2.54cm in Australia,
2.540005cm in the U.S.A.
and 2.5399956cm in the U.K.
AVOIRDUPOIS
The Avoirdupois weight system is the standard in The U.S.A.
Avoirdupois was widely used in most English-speaking countries for the general
weighing of goods,
except for precious metals, gems and drugs.
Just to refresh our memories, below is a chart of the main conversion factors in
the Avoirdupois system.
27.34375 grains = 1 dram
16 drams = 1 oz.
437.5 grains = 1 oz.
16 ozs. = 1 lb.
7,000 grains = 1 lb.
14 lb. = 1 stone
28 lb. = 1 qr.
4 qr. = 1 cwt.
112 lb. = 1 cwt.
20 cwt. = 1 ton
2,240 lb. = 1 ton
APOTHECARIES
The lesser known Apothecaries system, was widely used by Chemists and
Pharmacists,
for the compounding and dispensing of Drugs and Medicines.
20 grains = 1 scruple
3 scruples = 1 drachm
8 drachm = 1 oz. apoth.
1 oz. apoth. = 1 Troy oz.
N.B. The Apothecaries Ounce is equal to the TROY Ounce, but neither is equal to
the Avoirdupois Ounce.
TROY
Whilst the TROY system is reputedly not as old as Avoirdupois, it nonetheless
dates from Medieval Times,
where it was established at the celebrated Fair at TROYES in North Eastern
France.
The TROY oz. is still the official universal yardstick for the price of GOLD,
SILVER, PLATINUM
and other precious metals, quoted in U.S. Dollars per TROY Ounce.
In the late 1800's, BRITAIN abolished the TROY POUND as an official unit of
weight, but in the U.S.A. it continued
to be recognized until recent times.
24 grains = 1 dwt
20 dwt = 1 oz.
12 oz. = 1 lb.
480 grains = 1 oz.
5,760 grains = 1 lb.
N.B. That a TROY lb. is lighter than an AVOIRDUPOIS lb. - 5,760 grains compared
to 7,000 grains,
but a TROY oz. (480 grains) is heavier than an AVOIRDUPOIS oz.(437.5 grains).
What's heavier, a pound of Gold or a pound of Feathers ? The answer - you work
it out for yourself
THE GRAIN
One factor common amongst the three IMPERIAL weight systems, is that the base
unit of weight, the Grain,
is exactly equal in all three systems.
Starting from this common denominator, it can be appreciated that conversion is
a relatively simple matter,
amongst these three systems.
Historically, the Grain was established as a unit of weight in 1266, when Henry
III declared
that every English Penny should weigh the equivalent of 32 Grains of wheat,
"well dried and gathered from the middle of the ear".
One Grain in weight, of Alluvial GOLD, is about the size of a small match-head
or shotgun pellet.
The very accurate Scales sold by Gunshops, which are used to weigh powder for
reloading ammunition cases,
weigh in Grains.
1 Troy grain = 1 grain Apoth. = 1 Avoir. grain
1 Grain = 0.0648 Metric Grams
METRIC
The French are the instigators of what some describe as "a diabolical plot", but
which all rational people would agree,
is the only sensible weighing system in existence.
This decimal system of weights and measures was accepted into French Law in
1795.
It was subsequently adopted internationally, (well, by 17 European Countries),
at the Metric Convention in 1875.
The modern metric system was agreed to in 1960, and is known as the
"International System of Units (SI)".
Science has long used the metric system for its simplicity and universal
coverage.
1000 milligrams = 1 gram
1000 grams = 1 kg.
1000 kg. = 1 tonne (Metric Ton)
1 gram = 15.4323584 Troy grains
CARATS
Historically, most Precious Gems were also weighed in TROY, although it is now
common for stones such as Sapphire, Diamond,
Emerald, Ruby, Topaz, etc. to be weighed in CARATS.
Traditionally, the official standard of CARATS was reserved for weighing
Diamonds and Pearls. But pearls can also be weighed in the Japanese "Momme" 1
momme=3.75g
It has now been Internationally Standardized by the Diamond Trade, as the METRIC
CARAT.
One Carat being equal to one fifth of a gram (0.2g) and can also be subdivided
into 4 Diamond Grains
or split Decimally into 100 Points.
The CARAT was derived from the Arabic word qirrat and the Greek word kerat,
named after the seed of the Carob Tree.
When this seed is dried it has a remarkably uniform weight.
It was developed in ancient times by Middle Eastern Merchants,for the weighing
of Pearls.
1 Carat = 3.17 Troy Grains (Prior to the Metric Standard) OLD
1 Carat = 3.08647167 Troy Grains = 0.2 Metric Grams NEW
1 Carat = 100 Diamond Points
1 Carat = 4 Diamond Grains
The above CARAT has of course no relation to the CARAT (spelt KARAT in USA),
used for expressing the degree of purity of GOLD as used by the Jewelery Trade.
Pure GOLD is equal to 24 Carats and various metals can be alloyed with GOLD to
produce the required purity,
hardness, color, etc. such as SILVER, COPPER, PLATINUM and NICKEL.
24 Carat = 100.0 % Pure GOLD
22 Carat = 91.6 % " "
20 Carat = 83.3 % " "
18 Carat = 75.0 % " "
14 Carat = 58.3 % " "
12 Carat = 50.0 % " "
9 Carat = 37.5 % " "
BULLION
The International Bullion Trade has another method of defining the purity or
"Fineness" of GOLD,
and that is a scale from 0 to 1000 Fine.
The minimum fineness for bars of GOLD traded on the London GOLD Market is 995,
and many bars are refined to 999 or greater purity.
The standard size for GOLD Bullion is 400 TROY Oz.
Bars of this size are used for settling International Trade Debts and Commerce.
The Perth Mint and other Australian Refiners and Bullion Companies produce GOLD
Bullion Bars in various sizes,
usually ranging from 0.5 Troy Oz. to 400 ozs.
1000 Fine = 100 % Pure GOLD = 24 Carat
916.6 Fine = Australian & British Gold Sovereigns
500 Fine = 50 % Pure GOLD
The NOBLE METALS
The Precious, Noble or Rare Metals that are weighed in TROY include the
following:-
GOLD, SILVER, PLATINUM, OSMIUM, PALLADIUM, IRIDIUM, RUTHENIUM and RHODIUM.
This group of Metallic Elements gets its name from the physical property that
members of the group display
- that is, they are mostly chemically inert, resistant to rusting, oxidation or
acids,
and are thus Precious and Noble metals.
Their relative scarcity also has a degree of influence on their price.
Increasingly today, members of this group of metals are in great demand in
industry,
as new uses are being found and consumption generally outstrips supply.
SPECIFIC GRAVITY
The use of the Principle of Archimedes is the best known way to determine the
GOLD content
of a Specimen or Nugget.
The Specific Gravity of a Mineral or Specimen is its weight compared with water
(at standard temperature and pressure).
Water, which is taken as the base standard, has a Specific Gravity of 1.
Consequently, to determine the S.G. of a specimen, it is necessary to find its
weight
and that of a corresponding bulk of water, and to divide the first by the last.
Below is a Table of Specific Gravity for some of the main Minerals, Metals and
Gems
that may interest the average prospector in Australia and elsewhere.
GOLD = 19.3
PLATINUM = 21.46
PALLADIUM = 11.3 - 12.0
OSMIUM = 22.48 · The heaviest of all metals
IRIDIUM = 22.4
RHODIUM = 12.1
RUTHENIUM = 12.2
SILVER = 10.5
TELLURIUM = 6.2
CASSITERITE = 6.4 - 7.1
LEAD = 11.34
MERCURY = 13.6
QUARTZ = 2.65
SAPPHIRE = 4.0
DIAMOND = 3.5
ZIRCON = 4.0 - 4.7
GARNET = 3.1 - 4.3
TOPAZ = 3.5
GLOSSARY
dwt. = pennyweight
oz. = ounce
lb. = pound
qr. = quarter
cwt. = hundredweight
kg. = kilogram