In weighing the materials for a crucible charge the use of a set of assay-ton weights saves much labour in
calculation. The assay-ton is a
weight which contains as many milligrammes as a ton contains ounces.
Thus an English or long ton of 2,240 lb ... contains 32,666 Troy oz,
so that the corresponding assay-ton
must weigh ... 32.666 g. If the
weight of the resulting bead of gold (or silver) from an assay-ton of ore is 1.5 mg, then the ore
contains 1.5 oz of gold per statute ton.
If the value per short ton of 2,000 lb (used in North America) is required, the weight of
the assay-ton is 29.166 g, since
there are 29,166 Troy oz in 2,000 lb avoirdupois. (p. 441)
The Assay-Ton System —To
facilitate calculation a system of weights, known as the "assay-ton system" (abbreviated A.T.)
has been devised, which is a combination of the Troy and Avoirdupois systems
with the French metrical system. The unit of the system is the "assay-ton", which for the English
system (2,240 lb to the ton) is 32.6666 g. (p. 59)
(abbreviation 'AT') is not a unit of measurement, but a standard quantity
used in assaying ores of precious metals; it is 29+1⁄6 grams
(short assay ton) or 32+2⁄3
grams (long assay ton), the amount
which bears the same ratio to a milligram as a short or long ton bears to a
troy ounce. In other words, the number of
milligrams of a particular metal found in a sample of this size gives the
number of troy ounces contained in a short or long ton of ore.