substances.

(2) Kinds:
(_a_) _Borax._--This alkali is one of the
mildest, and for this reason is less harmful to
the clothing. It is useful when an alkali is
required to soften water for coloured clothes
or woollens. It also has a tendency to keep
white clothes a good colour.
(_b_) _Ammonia._--This also is a mild alkali,
but is apt to "yellow" white materials. As it
is very volatile, it should not be used unless
the washing can be done quickly.
(_c_) _Washing soda._--This is a cheap
substance and stronger than borax or ammonia.
It should be made into a solution before it is
used, for fear of too great strength.

(_d_) _Lye, or caustic soda._--This alkali is
very strong and should be employed with great
care. It must not be used except in weak
solutions, otherwise it would entirely dissolve
fabrics. It is not advisable for home laundry
work.

3. Soap:

(1) Use.--To act on greasy matter.

Soap-suds penetrate fabrics more completely
than water alone, and when the soap comes in
contact with fatty material, it _emulsifies_
it, that is, very finely divides it into minute
particles, so that it can be easily removed. If
a soap is used that contains free alkali, this
substance unites with the greasy impurities to
form new soap which has cleansing value.

(2) Kinds.--(_a_) Neutral, (_b_) medium, (_c_)
strong.

All soap is a compound of an alkali and fat,
and according as one or the other of these
substances predominates, the kind of soap is
determined.

When just enough alkali is used to completely
_saponify_ the amount of fat, the product is
called a neutral, or mild, soap. When an excess
of alkali is present, the soap is termed medium
or strong, according to the amount of free
alkali it contains.

A mild soap should be used when free alkali
would be injurious, as in washing woollens or
fabrics that have delicate colours.

4. Soap substitutes, or adjuncts:

(1) Use.-