the two systems are not the same. A ton contains 15,680,000 grains,
which equal 653,333.3 dwts. or 32,666.6 ozs. (troy). The following rules
are useful:--

To get ozs. (troy) per ton, multiply parts per 100,000 by 0.327;
To get dwts. per ton, multiply parts per 100,000 by 6.53;
To get grains per ton, multiply parts per 100,000 by 156.8.

Where liquids are being assayed, cubic centimetres are held to be
equivalent to grams, and the usual method of statement is, "so many
parts by weight in so many by measure." Where the statement is made as
grams per litre or grains per gallon, there can be no doubt as to what
is meant; and even if it be expressed in parts per 100,000, parts by
weight in a measured volume must be understood unless the contrary is
expressly stated.

In some cases, where the density of the solution differs greatly from
that of water, the percentage by weight may be given; and in others,
mixtures of two or more liquids, the percentages may be given by volume
or by weight; as so many c.c. in 100 c.c., or as so many grams in 100
grams, or even as so many grams in 100 c.c. In such cases it must be
distinctly shown which method of statement is adopted.

One grain per gallon means 1 grain in 70,000 grain-measures, or one part
in 70,000. Dividing by 7 and multiplying by 10 will convert grains per
gallon into parts per 100,000. Inversely, dividing by 10 and multiplying
by 7, will convert parts per 100,000 into grains per gallon.

Grams per litre are parts per 1000; multiplying by 100 will give parts
per 100,000, and multiplying by 70 will give grains per gallon.