In our endeavour to establish the claims of the science of chemistry to
a prominent place in the educational equipment of women, all reference
to those most interesting and important chemical phenomena that
accompany the exercise of the physiological functions will be omitted;
as also those which are most immediately concerned with the preparation
of food. Attention will be confined to some of the common occurrences of
daily life, the methods of dealing with which are typical of the method
adopted in considering more important and abstruse problems.
Perhaps one of the most disappointing experiences of the novice in
housekeeping is the rapidity with which everything assumes a shabby
aspect. Bright paint grows dull, dull paint wears away, curtains and
fabrics fade, and very soon mistress and maids alike feel that the
house no longer repays the trouble incurred in the spring-cleaning
that it must still undergo. This spring-cleaning, the primary object
of which is the preservation of the beauty and substance of the house
and its appointments, is in the result the cause of much of their
deterioration.
Cleaning consists in removing dirt by means that are partly physical and
partly chemical; for instance, the removal of dust by sweeping, shaking,
or brushing is a physical operation, and the removal of dirt and grease
by dissolving them in soapy water involves their change by a chemical
process. If the surfaces or materials to be cleaned include a substance
on which the cleansing agent can operate the agent will not confine its
work to the removal of the dirt only; in washing coloured fabrics we
know how often the colour comes out with the dirt. Knowledge therefore,
not only of the composition and properties of cleansing agents, but also
of the surfaces and materials to which they are to be applied, is
essential, and we should find that it is not always the powder or paste
which makes the greatest show of cleanliness in the shortest time, with
least expenditure of labour, that is the most to be desired.
_The use of alkalies._--The most common cleansing agents are hot water,
soap, and soda. Hot water is itself a detergent; that is, it has the
power of dissolving dirt. It does not, however, dissolve grease, and all
household dirt is more or less greasy, hence we cannot do our cleansing
with water only, and we are accustomed to add to it soap or soda.
It is not easy or even possible to discuss the chemical properties of
substances without the use of chemical terms. Substances are
classified for chemical purposes in groups, every member of which
exhibits the same chemical property, and we shall require to distinguish
between the group called acids and the group called alkalies. It
will be sufficient for our purpose just now to know that acids have a
sour taste and that alkalies counteract acids. From this definition
lemon-juice will easily be recognised as an acid. If we add soda to
lemon-juice there will be a brisk effervescence and the lemon-juice
will no longer be sour, hence soda is an alkali. Alkalies have
another well-known chemical property--they dissolve grease and oil and
enable them to mix with water. If we have some hot water in a
tumbler and pour oil into it the oil will float on the water, and if
we stir the two together the oil will break into globules but will still
float on the water; we cannot mix them together. If we dissolve some
soda in hot water and pour in oil we shall find on stirring that the
mixture becomes milky or soapy in appearance and the oil and water are
no longer discernible as different fluids. Moreover, on standing the
oil will not again separate from the water; it has been emulsified.
Oils themselves have the chemical power of dissolving resins. Resins
are hard, bright vegetable gums which will come under our notice when
we consider the composition of varnishes.
All hard soaps are made from soda, grease, and resin; the cheaper soaps
contain free soda, the dearer ones contain an excess of fat. Yellow
scrubbing soap contains about eight per cent. of free soda. Both soap
and soda can be dissolved in water, and are so dissolved for cleaning
purposes. Knowing the constituents of our cleansing agents, we can
consider their action on paint and varnish. Paint contains white-lead,
linseed-oil, and colouring matter. It is not very hard when dry and can
be easily scratched with the nail. Varnish is made from linseed-oil,
resin, and turpentine. When dry it should be very hard and bright.
The whole of the painted woodwork of the house is subjected to
spring-cleaning whatever its appearance with regard to dirt may be. The
operator throws into a pailful of hot water a "handful" of soda, soaks a
scrubbing-brush in the mixture, rubs it well with soap, and uses it to
brush the somewhat soft paint or harder varnish. The soda and soap,
aided by the heat, soften the paint and the brush removes a quantity
equal to about a coat of paint. The effect is certainly pleasing for the
time being, but there will be no difficulty in understanding that the
process can only be repeated until the paint and varnish grow shabby or
disappear.
It is not wise for the inexpert housewife to trust to unscientific
friends for advice as to the best materials to use when cleaning paint.
A foreman painter once gave, as a recipe for this purpose, an
instruction to add a tablespoonful of "salts of tartar" to
three-quarters of a pailful of water. The result was a very rapid and
complete removal of dirt from the paint, but the housewife, being
dissatisfied with the rather dull appearance of the white varnish,
stroked it with her finger and found that it was covered with a fine
white powder. The maid's assurance that this was all right and only
needed to be removed by dusting did not satisfy her, and she began to
wonder what chemical action was to be expected from "salts of tartar." A
first search for information revealed that salts of tartar was an old
name for "potassium carbonate," but the housewife knew no chemistry and
had never heard of potassium carbonate, so this information was useless
to her. She had, however, had some scientific training and was not
satisfied to rest in ignorance. A search in a book on elementary
chemistry disclosed the further truth that the commercial name for
"potassium carbonate" is pearlash! She then remembered that being
desirous at one time to remove the paint from some oak carving said to
be two hundred years' old, she had successfully used a solution of
pearlash painted on with a brush. The paint when dry from the
application had been scraped off in long, tough ribbons. Of course the
mixture had been very much stronger than that prescribed by the painter,
but the effect had been very much more apparent.
Acids and alkalies are to some extent responsible for the fading of
fabrics in the wash when these fabrics owe their colour to vegetable
dyes. Acids turn vegetable blues red, alkalies turn vegetable blues
green and vegetable yellows brown. It is easy to illustrate this action
of acids and alkalies on vegetable colours. A blue liquid can be
obtained by boiling a red cabbage in water. If we take two portions of
this water and add any acid, say lemon-juice, to one portion we shall
obtain a red liquid; if we add any alkali, say soda, to the other
portion we shall obtain a green liquid. If we go a step further and add
lemon-juice to the green liquid and soda to the red liquid we may
approach very nearly to our original blue liquid. These experiments
suggest a remedy for the change of colour in fabrics on washing with
soda, but the dyes most commonly used are not vegetable dyes, and the
fading of the fabrics is due to chemical changes, into which we have no
space to enter.
Strong acids and alkalies act as caustics; that is they destroy fabrics.
Continued washing in strong soda and water not only tends to destroy,
but also spoils the appearance of all kinds of wearing apparel and
household linen. White silk and wool at once become yellow on being
washed with soap that contains free soda, and linen is affected in the
same way though not to the same extent.
The widely advertised pastes and liquids for cleaning metal-work,
particularly brass, often contain acids or alkalies that are injurious
to metals. If after cleaning there should be a green deposit on brass or
copper it will be wise to inquire into the composition of such deposit,
and to discontinue the use of that paste or liquid. When brass pans are
used for boiling fruit for jams, it is usual to rub them inside with a
slice of lemon before putting in the fruit. A careful housewife will
consider the reason for this custom. We remember once seeing a copper
pan, that had been provided for the preparation of oatmeal porridge,
with a band about an inch wide of green crystals on the inside. Inquiry
elicited that the cook had thought it a convenient pan in which to
prepare the fish (salt haddock) for breakfast. Ignorance of the chemical
action of salt and acids on metals may lead to very serious results. The
common name for the green deposit on brass and copper is verdigris, and
most people know that verdigris is a poisonous compound; the difficulty
is that, not knowing its chemical composition, they do not recognise
verdigris when they see it. The cook thought that the complaint made had
reference only to the misuse of the pan, and said that it was quite easy
to clean the green deposit off!