MAN'S CONQUEST OF SUBSTANCES
201. Chemistry. Man's mechanical inventions have been equaled by his
chemical researches and discoveries, and by the application he has
made of his new knowledge.
The plain cotton frock of our grandmothers had its death knell sounded
a few years ago, when John Mercer showed that cotton fabrics soaked in
caustic soda assumed under certain conditions a silky sheen, and when
dyed took on beautiful and varied hues. The demonstration of this
simple fact laid the foundation for the manufacture of a vast variety
of attractive dress materials known as mercerized cotton.
Possibly no industry has been more affected by chemical discovery than
that of dyeing. Those of us who have seen the old masterpieces in
painting, or reproductions of them, know the softness, the mellowness,
the richness of tints employed by the old masters. But if we look for
the brilliancy and variety of color seen in our own day, the search
will be fruitless, because these were unknown until a half century
ago. Up to that time, dyes were few in number and were extracted
solely from plants, principally from the indigo and madder plants. But
about the year 1856 it was discovered that dyes in much greater
variety and in purer form could be obtained from coal tar. This
chemical production of dyes has now largely supplanted the original
method, and the industry has grown so rapidly that a single firm
produced in one year from coal tar a quantity of indigo dye which
under the natural process of plant extraction would have required a
quarter million acres of indigo plant.
The abundance and cheapness of newspapers, coarse wrapping papers,
etc., is due to the fact that man has learned to substitute wood for
rags in the manufacture of paper. Investigation brought out the fact
that wood contained the substance which made rags valuable for paper
making. Since the supply of rags was far less than the demand, the
problem of the extraction from wood of the paper-forming substance was
a vital one. From repeated trials, it was found that caustic soda when
heated with wood chips destroyed everything in the wood except the
desired substance, cellulose; this could be removed, bleached, dried,
and pressed into paper. The substitution of wood for rags has made
possible the daily issue of newspapers, for the making of which
sufficient material would not otherwise have been available. When we
reflect that a daily paper of wide circulation consumes ten acres of
wood lot per day, we see that all the rags in the world would be
inadequate to meet this demand alone, to say nothing of periodicals,
books, tissue paper, etc.
Chemistry plays a part in every phase of life; in the arts, the
industries, the household, and in the body itself, where digestion,
excretion, etc., result from the action of the bodily fluids upon
food. The chemical substances of most interest to us are those which
affect us personally rather than industrially; for example, soap,
which cleanses our bodies, our clothing, our household possessions;
washing soda, which lightens laundry work; lye, which clears out the
drain pipe clogged with grease; benzine, which removes stains from
clothing; turpentine, which rids us of paint spots left by careless
workmen; and hydrogen peroxide, which disinfects wounds and sores.
In order to understand the action of several of these substances we
must study the properties of two groups of chemicals--known
respectively as acids and bases; the first of these may be represented
by vinegar, sulphuric acid, and oxalic acid; and the second, by
ammonia, lye, and limewater.
202. Acids. All of us know that vinegar and lemon juice have a sour
taste, and it is easy to show that most acids are characterized by a
sour taste. If a clean glass rod is dipped into very dilute acid, such
as acetic, sulphuric, or nitric acid, and then lightly touched to the
tongue, it will taste sour. But the best test of an acid is by sight
rather than by taste, because it has been found that an acid is able
to discolor a plant substance called litmus. If paper is soaked in a
litmus solution until it acquires the characteristic blue hue of the
plant substance, and is then dried thoroughly, it can be used to
detect acids, because if it comes in contact with even the minutest
trace of acid, it loses its blue color and assumes a red tint. Hence,
in order to detect the presence of acid in a substance, one has merely
to put some of the substance on blue litmus paper, and note whether or
not the latter changes color. This test shows that many of our common
foods contain some acid; for example, fruit, buttermilk, sour bread,
and vinegar.
The damage which can be done by strong acids is well known; if a jar
of sulphuric acid is overturned, and some of it falls on the skin, it
eats its way into the flesh and leaves an ugly sore; if it falls on
carpet or coat, it eats its way into the material and leaves an
unsightly hole. The evil results of an accident with acid can be
lessened if we know just what to do and do it quickly, but for this we
must have a knowledge of bases, the second group of chemicals.
203. Bases. Substances belonging to this group usually have a bitter
taste and a slimy, soapy feeling. For our present purposes, the most
important characteristic of a base is that it will neutralize an acid
and in some measure hinder the damage effected by the former. If, as
soon as an acid has been spilled on cloth, a base, such as ammonia, is
applied to the affected region, but little harm will be done. In your
laboratory experiments you may be unfortunate enough to spill acid on
your body or clothing; if so, quickly apply ammonia. If you delay, the
acid does its work, and there is no remedy. If soda (a base) touches
black material, it discolors it and leaves an ugly brown spot; but the
application of a little acid, such as vinegar or lemon juice, will
often restore the original color and counteract the bad effects of the
base. Limewater prescribed by physicians in cases of illness is a
well-known base. This liquid neutralizes the too abundant acids
present in a weak system and so quiets and tones the stomach.
The interaction of acids and bases may be observed in another way. If
blue litmus paper is put into an acid solution, its color changes to
red; if now the red litmus paper is dipped into a base solution,
caustic soda, for example, its original color is partially restored.
What the acid does, the base undoes, either wholly or in part. Bases
always turn red litmus paper blue.
Bases, like acids, are good or bad according to their use; if they
come in contact with cloth, they eat or discolor it, unless
neutralized by an acid. But this property of bases, harmful in one
way, is put to advantage in the home, where grease is removed from
drainpipe and sink by the application of lye, a strong base. If the
lye is too concentrated, it will not only eat the grease, but will
corrode the metal piping; it is easy, however, to dilute base
solutions to such a degree that they will not affect piping, but will
remove grease. Dilute ammonia is used in almost every home and is an
indispensable domestic servant; diluted sufficiently, it is
invaluable in the washing of delicate fabrics and in the removing of
stains, and in a more concentrated form it is helpful as a smelling
salt in cases of fainting.
Some concentrated bases are so powerful in their action on grease,
cloth, and metal that they have received the designation _caustic_,
and are ordinarily known as caustic soda, caustic potash (lye), and
caustic lime. These more active bases are generally called alkalies in
distinction from the less active ones.
204. Neutral Substances. To any acid solution add gradually a small
quantity of a base, and test the mixture from time to time with blue
litmus paper; at first the paper will turn red quickly, but as more
and more of the base is added to the solution, it has less and less
effect on the blue litmus paper, and finally a point is reached when a
fresh strip of blue paper will not be affected. Such a result
indicates infallibly the absence of any acid qualities in the
solution. If now red litmus paper is tested in the same solution, its
color also will remain unchanged; such a result indicates infallibly
the absence of any basic quality. The solution has the characteristic
property of neither acid nor base and is said to be neutral.
If to the neutral solution an extra portion of base is added, so that
there is an excess of base over acid, the neutralization is
overbalanced and the red paper turns blue. If to the neutral solution
an extra portion of acid is added, so that there is an excess of acid
over base, the neutralization is overbalanced in the opposite
direction, and the solution acquires acid characteristics.
Most acids and bases will eat and corrode and discolor, while neutral
substances will not; it is for this reason that soap, a slightly
alkaline substance, is the safest cleansing agent for laundry, bath,
and general work. Good soaps, being carefully made, are so nearly
neutral that they will not fade the color out of clothing; the cheap
soaps are less carefully prepared and are apt to have a strong excess
of the base ingredient; such soaps are not safe for delicate work.
205. Soap. If we gather together scrapings of lard, butter, bits of
tallow from burned-out candles, scraps of waste fat, or any other sort
of grease, and pour a strong solution of lye over the mass, a soft
soapy substance is formed. In colonial times, every family made its
own supply of soap, utilizing, for that purpose, household scraps
often regarded by the housekeeper of to-day as worthless. Grease and
fat were boiled with water and hardwood ashes, which are rich in lye,
and from the mixture came the soft soap used by our ancestors. In
practice, the wood ashes were boiled in water, which was then strained
off, and the resulting filtrate, or lye, was mixed with the fats for
soap making.
Most fats contain a substance of an acid nature, and are decomposed by
the action of bases such as caustic soda and caustic potash. The acid
component of the grease partially neutralizes the base, and a new
substance is formed, namely, soap.
With the advance of civilization the labor of soap making passed from
the home to the factory, very much as bread making has done in our own
day. Different varieties of soaps appeared, of which the hard soap was
the most popular, owing to the ease with which it could be
transported. Within the last few years liquid soaps have come into
favor, especially in schools, railroad stations, and other public
places, where a cake of soap would be handled by many persons. By
means of a simple device (Fig. 157), the soap escapes from a
receptacle when needed. The mass of the soap does not come in contact
with the skin, and hence the spread of contagious skin diseases is
lessened.
[Illustration: FIG. 157.--Liquid soap container.]
Commercial soaps are made from a great variety of substances, such as
tallow, lard, castor oil, coconut oil, olive oil, etc.; or in cheaper
soaps, from rosin, cottonseed oil, and waste grease. The fats which go
to waste in our garbage could be made a source of income, not only to
the housewife, but to the city. In Columbus, Ohio, garbage is used as
a source of revenue; the grease from the garbage being sold for soap
making, and the tankage (Section 188) for fertilizer.
206. Why Soap Cleans. The natural oil of the skin catches and
retains dust and dirt, and makes a greasy film over the body. This
cannot be removed by water alone, but if soap is used and a generous
lather is applied to the skin, the dirt is "cut" and passes from the
body into the water. Soap affects a grease film and water very much as
the white of an egg affects oil and water. These two liquids alone do
not mix, the oil remaining separate on the surface of the water; but
if a small quantity of white of egg is added, an emulsion is formed,
the oil separating into minute droplets which spread through the
water. In the same way, soap acts on a grease film, separating it into
minute droplets which leave the skin and spread through the water,
carrying with them the dust and dirt particles. The warmer the water,
the better will be the emulsion, and hence the more effective the
removal of dirt and grease. This explanation holds true for the
removal of grease from any surface, whether of the body, clothing,
furniture, or dishes.
207. Washing Powders. Sometimes soap refuses to form a lather and
instead cakes and floats as a scum on the top of the water; this is
not the fault of the soap but of the water. As water seeps through
the soil or flows over the land, it absorbs and retains various soil
constituents which modify its character and, in some cases, render it
almost useless for household purposes. Most of us are familiar with
the rain barrel of the country house, and know that the housewife
prefers rain water for laundry and general work. Rain water, coming as
it does from the clouds, is free from the chemicals gathered by ground
water, and is hence practically pure. While foreign substances do not
necessarily injure water for drinking purposes (Section 69), they are
often of such a nature as to prevent soap from forming an emulsion,
and hence from doing its work. Under such circumstances the water is
said to be hard, and soap used with it is wasted. Even if water is
only moderately hard, much soap is lost. The substances which make
water hard are calcium and magnesium salts. When soap is put into
water containing one or both of these, it combines with the salts to
form sticky insoluble scum. It is therefore not free to form an
emulsion and to remove grease. As a cleansing agent it is valueless.
The average city supply contains so little hardness that it is
satisfactory for toilet purposes; but in the laundry, where there is
need for the full effect of the soap, and where the slightest loss
would aggregate a great deal in the course of time, something must be
done to counteract the hardness. The addition of soda, or sodium
carbonate to the water will usually produce the desired effect.
Washing soda combines with calcium and magnesium and prevents them
from uniting with soap. The soap is thus free to form an emulsion,
just as in ordinary water. Washing powders are sometimes used instead
of washing soda. Most washing powders contain, in addition to a
softening agent, some alkali, and hence a double good is obtained from
their use; they not only soften the water and allow the soap to form
an emulsion, but they also, through their alkali content, cut the
grease and themselves act as cleansers. In some cities where the water
is very hard, as in Columbus, Ohio, it is softened and filtered at
public expense, before it leaves the reservoirs. But even under these
circumstances, a moderate use of washing powder is general in laundry
work.
If washing powder is put on clothes dry, or is thrown into a crowded
tub, it will eat the clothes before it has a chance to dissolve in the
water. The only safe method is to dissolve the powder before the
clothes are put into the tub. The trouble with our public laundries is
that many of them are careless about this very fact, and do not take
time to dissolve the powder before mixing it with the clothes.
The strongest washing powder is soda, and this cheap form is as good
as any of the more expensive preparations sold under fancy names.
Borax is a milder powder and is desirable for finer work.
One of the most disagreeable consequences of the use of hard water for
bathing is the unavoidable scum which forms on the sides of bathtub
and washbowl. The removal of the caked grease is difficult, and if
soap alone is used, the cleaning of the tub requires both patience and
hard scrubbing. The labor can be greatly lessened by moistening the
scrubbing cloth with turpentine and applying it to the greasy film,
which immediately dissolves and thus can be easily removed. The
presence of the scum can be largely avoided by adding a small amount
of liquid ammonia to the bath water. But many persons object to this;
hence it is well to have some other easy method of removing the
objectionable matter.
208. To remove Stains from Cloth. While soap is, generally speaking,
the best cleansing agent, there are occasions when other substances
can be used to better advantage. For example, grease spots on carpet
and non-washable dress goods are best removed by the application of
gasoline or benzine. These substances dissolve the grease, but do not
remove it from the clothing; for that purpose a woolen cloth should be
laid under the stain in readiness to absorb the benzine and the grease
dissolved in it. If the grease is not absorbed while in solution, it
remains in the clothing and after the evaporation of the benzine
reappears in full force.
Cleaners frequently clean suits by laying a blotter over a grease spot
and applying a hot iron; the grease, when melted by the heat, takes
the easiest way of spreading itself and passes from cloth to blotter.
209. Salts. A neutral liquid formed as in Section 204, by the action
of hydrochloric acid and the alkali solution of caustic soda, has a
brackish, salty taste, and is, in fact, a solution of salt. This can
be demonstrated by evaporating the neutral liquid to dryness and
examining the residue of solid matter, which proves to be common salt.
When an acid is mixed with a base, the result is a substance more or
less similar in its properties to common salt; for this reason all
compounds formed by the neutralization of an acid with a base are
called salts. If, instead of hydrochloric acid (HCl), we use an acid
solution of potassium tartrate, and if instead of caustic soda we use
bicarbonate of soda (baking soda), the result is a brackish liquid as
before, but the salt in the liquid is not common salt, but Rochelle
salt. Different combinations of acids and bases produce different
salts. Of all the vast group of salts, the most abundant as well as
the most important is common salt, known technically as sodium
chloride because of its two constituents, sodium and chlorine.
We are not dependent upon neutralization for the enormous quantities
of salt used in the home and in commerce. It is from the active,
restless seas of the present, and from the dead seas of the
prehistoric past that our vast stores of salt come. The waters of the
Mediterranean and of our own Great Salt Lake are led into shallow
basins, where, after evaporation by the heat of the sun, they leave a
residue of salt. By far the largest quantity of salt, however, comes
from the seas which no longer exist, but which in far remote ages
dried up and left behind them their burden of salt. Deposits of salt
formed in this way are found scattered throughout the world, and in
our own country are found in greatest abundance in New York. The
largest salt deposit known has a depth of one mile and exists in
Germany.
Salt is indispensable on our table and in our kitchen, but the amount
of salt used in this way is far too small to account for a yearly
consumption of 4,000,000 tons in the United States alone. The
manufacture of soap, glass, bleaching powders, baking powders, washing
soda, and other chemicals depends on salt, and it is for these that
the salt beds are mined.
210. Baking Soda. Salt is by all odds the most important sodium
compound. Next to it come the so-called carbonates: first, sodium
carbonate, which is already familiar to us as washing soda; and
second, sodium bicarbonate, which is an ingredient of baking powders.
These are both obtained from sodium chloride by relatively simple
means; that is, by treating salt with the base, ammonia, and with
carbon dioxide.
Washing soda has already been discussed. Since baking powders in some
form are used in almost all homes for the raising of cake and pastry
dough, it is essential that their helpful and harmful qualities be
clearly understood.
The raising of dough by means of baking soda--bicarbonate of soda--is
a very simple process. When soda is heated, it gives off carbon
dioxide gas; you can easily prove this for yourself by burning a
little soda in a test tube, and testing the escaping gas in a test
tube of limewater. When flour and water alone are kneaded and baked
in loaves, the result is a mass so compact and hard that human teeth
are almost powerless to crush and chew it. The problem is to separate
the mass of dough or, in other words, to cause it to rise and lighten.
This can be done by mixing a little soda in the flour, because the
heat of the oven causes the soda to give off bubbles of gas, and these
in expanding make the heavy mass slightly porous. Bread is never
lightened with soda because the amount of gas thus given off is too
small to convert heavy compact bread dough into a spongy mass; but
biscuit and cake, being by nature less compact and heavy, are
sufficiently lightened by the gas given off from soda.
But there is one great objection to the use of soda alone as a
leavening agent. After baking soda has lost its carbon dioxide gas, it
is no longer baking soda, but is transformed into its relative,
washing soda, which has a disagreeable taste and is by no means
desirable for the stomach.
Man's knowledge of chemicals and their effect on each other has
enabled him to overcome this difficulty and, at the same time, to
retain the leavening effect of the baking soda.
211. Baking Powders. If some cooking soda is put into lemon juice or
vinegar, or any acid, bubbles of gas immediately form and escape from
the liquid. After the effervescence has ceased, a taste of the liquid
will show you that the lemon juice has lost its acid nature, and has
acquired in exchange a salty taste. Baking soda, when treated with an
acid, is transformed into carbon dioxide and a salt. The various
baking powders on the market to-day consist of baking soda and some
acid substance, which acts upon the soda, forces it to give up its
gas, and at the same time unites with the residue to form a harmless
salt.
Cream of tartar contains sufficient acid to act on baking soda, and is
a convenient and safe ingredient for baking powder. When soda and
cream of tartar are mixed dry, they do not react on each other,
neither do they combine rapidly in _cold_ moist dough, but as soon as
the heat of the oven penetrates the doughy mass, the cream of tartar
combines with the soda and sets free the gas needed to raise the
dough. The gas expands with the heat of the oven, raising the dough
still more. Meanwhile, the dough itself is influenced by the heat and
is stiffened to such an extent that it retains its inflated shape and
spongy nature.
Many housewives look askance at ready-made baking powders and prefer
to bake with soda and sour milk, soda and buttermilk, or soda and
cream of tartar. Sour milk and buttermilk are quite as good as cream
of tartar, because the lactic acid which they contain combines with
the soda and liberates carbon dioxide, and forms a harmless residue in
the dough.
The desire of manufacturers to produce cheap baking powders led to the
use of cheap acids and alkalies, regardless of the character of the
resulting salt. Alum and soda were popular for some time; but careful
examination proved that the particular salt produced by this
combination was not readily absorbed by the stomach, and that its
retention there was injurious to health. For this reason, many states
have prohibited the use of alum in baking powders.
It is not only important to choose the ingredients carefully; it is
also necessary to calculate the respective quantities of each,
otherwise there will be an excess of acid or alkali for the stomach to
take care of. A standard powder contains twice as much cream of tartar
as of bicarbonate of soda, and the thrifty housewife who wishes to
economize, can make for herself, at small cost, as good a baking
powder as any on the market, by mixing tartar and soda in the above
proportions and adding a little corn starch to keep the mixture dry.
The self-raising flour, so widely advertised by grocers, is flour in
which these ingredients or their equivalent have been mixed by the
manufacturer.
212. Soda Mints. Bicarbonate of soda is practically the sole
ingredient of the soda mints popularly sold for indigestion. These
correct a tendency to sour stomach because they counteract the surplus
acid in the stomach, and form with it a safe neutral substance.
Seidlitz powder is a simple remedy consisting of two powders, one
containing bicarbonate of soda, and the other, some acid such as cream
of tartar. When these substances are dissolved in water and mixed,
effervescence occurs, carbon dioxide escapes, and a solution of
Rochelle salt remains.
212_a_. Source of Soda. An enormous quantity of sodium carbonate, or
soda, as it is usually called, is needed in the manufacture of glass,
soap, bleaching powders, and other commercial products. Formerly, the
supply of soda was very limited because man was dependent upon natural
deposits and upon ashes of sea plants for it. Common salt, sodium
chloride, is abundant, and in 1775 a prize was offered to any one who
would find a way to obtain soda from salt. As a result of this, soda
was soon manufactured from common salt. In the most recent methods of
manufacture, salt, water, ammonia, and carbon dioxide are made to
react. Baking soda is formed from the reaction. The baking soda is
then heated and decomposed into washing soda or the soda of commerce.