In the manufacture of embroidery fine threads of silver gilt are used.
To produce these, a bar of silver, weighing 180 ounces, is gilt with
an ounce of gold; this bar is then wire-drawn until it is reduced to a
thread so fine that 3400 feet of it weigh less than an ounce. It is
then flattened by being submitted to a severe pressure between
rollers, in which process its length is increased to 4000 feet. Each
foot of the flattened wire weighs, therefore, the 4000th part of an
ounce. But as in the processes of wire-drawing and rolling the
proportion of the two metals is maintained, the gold which covers the
surface of the fine thread thus produced consists only of the 180th
part of its whole weight. Therefore the gold which covers one foot is
only the 720,000th part of an ounce, and consequently the gold which
covers an inch will be the 8,640,000th part of an ounce. If this inch
be again divided into 100 equal parts, each part will be distinctly
visible without the aid of a microscope, and yet the gold which covers
such visible part will be only the 864,000,000th part of an ounce. But
we need not stop even here. This portion of the wire may be viewed
through a microscope which magnifies 500 times; and by these means,
therefore, its 500th part will become visible.--_Lardner's Handbook_.