_x_ = 1.008 gram.

This result, 1.008 gram, is the "_standard_." When a gas is measured,
the standard may be calculated in the same way. For example: with 0.224
gram of zinc, 75.8 c.c. of gas were obtained. Then the quantity of zinc
equivalent to 100 c.c. of the gas is got by the proportion.

75.8 : 0.224 :: 100 : _x_
_x_ = 0.2955 gram.

Using the term "standard" in this sense, the following rules hold
good:--

To find the weight of metal in a given substance:--_Multiply the
standard by the number of c.c. used and divide by 100._ For example: a
piece of zinc was dissolved and the gas evolved measured 73.9 c.c. Then
by the rule, 0.2955◊73.9/100 should give the weight of the piece of
zinc. This gives 0.2184 gram.

To find the percentage of metal in a given substance:--_Multiply the
standard by the number of c.c. used and divide by the weight of
substance taken._ For example: if 2 grams of a mineral were taken, and
if on titrating with the permanganate solution (standard 1.008) 60.4
c.c. were required, then (1.008◊60.4)/2 = 30.44. This is the
percentage.

If the standard is exactly 1 gram, and 1 gram of ore is always taken,
these calculations become very simple. The "c.c." used give at once the
percentage, or divided by 100 give the weight of metal.