way, the color
pattern is automatically printed on the cloth with perfect regularity.
In cases where the fabrics do not unite directly with the coloring
matter, the design is supplied with a mordant and the impression made
on the fabric is that of the mordant; when the fabric is later
transferred to a dye bath, the mordanted portions, represented by the
design, unite with the coloring matter and thus form the desired color
patterns.

Unless the printing is well done, the coloring matter does not
thoroughly penetrate the material, and only a faint blurred design
appears on the back of the cloth; the gaudy designs of cheap calicoes
and ginghams often do not show at all on the under side. Such
carelessly made prints are not fast to washing or light, and soon
fade. But in the better grades of material the printing is well done,
and the color designs are fairly fast, and a little care in the
laundry suffices to eliminate any danger of fading.

Color designs of the greatest durability are produced by the weaving
together of colored yarns. When yarn is dyed, the coloring matter
penetrates to every part of the fiber, and hence the patterns formed
by the weaving together of well-dyed yarns are very fast to light and
water.

If the color designs to be woven in the cloth are intricate, complex
machinery is necessary and skillful handwork; hence, patterns formed
by the weaving of colored yarns are expensive and less common than
printed fabrics.

CHAPTER XXIV

CHEMICALS AS DISINFECTANTS AND PRESERVATIVES

231. The prevention of disease epidemics is one of the most striking
achievements of modern science. Food, clothing, furniture, and other
objects contaminated in any way by disease germs may be disinfected by
chemicals or by heat, and widespread infection from persons suffering
with a contagious disease may be prevented.

[Illustration: FIG. 160.--Pasteurizing apparatus, an arrangement by
which milk is conveniently heated to destroy disease germs.]

When disease germs are within the body, the problem is far from
simple, because chemicals which would effectively destroy the germs
would be fatal to life itself. But when germs are outside the body, as
in water or milk, or on clothing, dishes, or furniture, they can be
easily killed. One of the best methods of destroying germs is to
subject them to intense heat. Contaminated water is made safe by
boiling for a few minutes, because the strong heat destroys the
disea