" 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.
Among foreign systems of weights, the French is by far the best.
Kilograms (2.205 lbs.) per quintal (220.5 lbs.) are parts per cent.; and
grams (15.43 grs.) per quintal are parts per 100,000. From the rule
already given, grams per quintal may be converted into ounces to the ton
by multiplying by 0.
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