Chapter LX: Section 58: Analysis

How can people tell what things are made of?

If it were not for chemical analysis, most of the big factories would have to shut down, much of our agricultural experimentation would stop, the Pure Food Law would be impossible to enforce, mining would be paralyzed, and the science of chemistry would almost vanish.

Analysis is finding out what things are made of. In order to make steel from ore, the ore has to be analyzed; and factories could not run very well without steel. In order to test soil, to test cow's milk, or to find the food value of different kinds of feed, analysis is essential. As to the Pure Food Law, how could the government find out that a firm was using artificial coloring matter or preservatives if there were no way of analyzing the food? In mining, the ore must be assayed; that is, it must be analyzed to show what part of it is gold, for instance, and what part consists of other minerals. Also, the analysis must show what these substances are, so that they can be treated properly. And the science of chemistry is largely the science of analyzing--finding out what things are made of and how they will act on each other.

The subject of chemical analysis is extremely important. But in this course it is impossible and unnecessary for you to learn to analyze everything; the main thing is for you to know what analysis is and to have a general notion of how a chemist analyzes things.

When you tested a number of substances with litmus paper to find out which of them were acids, you were really doing some work in chemical analysis. Chemists actually use litmus paper in this way to find out whether a substance is an acid or a base.

THE BORAX BEAD TEST. This is another chemical test, by which certain substances can be recognized:

EXPERIMENT 113. Make a loop of wire about a quarter of an inch
across, using light-weight platinum wire (about No. 30). Seal
the straight end of the wire into the end of a piece of glass
tubing by melting the end of the tube around the wire.

Hold the loop of wire in the flame of a Bunsen burner for
a few seconds, then dip the looped end in borax powder. Be
careful not to get borax on the upper part of the wire or on
the handle. Some of the borax will stick to the hot loop. Hold
this in the flame until it melts into a glassy bead in the
loop. You may have to dip it into the borax once or twice more
to get a good-sized bead.

When the bead is all glassy, and while it is melted, touch it
lightly to _one small grain_ of one of the chemicals on the
"jewel-making plate." This jewel-making plate is a plate
with six small heaps of chemicals on it. They are: manganese
dioxid, copper sulfate, cobalt chlorid, nickel salts, chrome
alum, and silver nitrate. Put the bead back into the flame
and let it melt until the color of the chemical has run all
through it. Then while it is still melted, shake the bead out
of the loop on to a clean plate. If it is dark colored and
cloudy, try again, getting a still smaller grain of the
chemical. You should get a bead that is transparent, but
clearly colored, like an emerald, topaz, or sapphire.

Repeat with each of the six chemicals, so that you have a set
of six different-colored beads.

This is a regular chemical test for certain elements when they are combined with oxygen. The cobalt will always change the borax bead to the blue you got; the chromium will make the bead emerald green or, in certain kinds of flame, ruby red; etc. If you wanted to know whether or not certain substances contained cobalt combined with oxygen, you could really find out by taking a grain on a borax bead and seeing if it turned blue.

THE HYDROCHLORIC ACID TEST FOR SILVER. The experiment in which you tested the action of light in effecting chemical change, and in which you made a white powder or precipitate in a silver nitrate solution by adding hydrochloric acid (page 327), is a regular chemical test to find out whether or not a thing has silver in it. If any silver is dissolved in nitric acid, you will get a precipitate (powder) when hydrochloric acid is added. Make the test in the following experiment:

EXPERIMENT 114. _Use distilled water all through this
experiment if possible._ First wash two test tubes and an
evaporating dish thoroughly, rinsing them several times. Into
one test tube pour some nitric acid diluted 1 to 4. Heat this
to boiling, then add a few drops of hydrochloric acid diluted
1 to 10. Does anything happen? Pour out this acid and rinse
the dish thoroughly. Now put a piece of silver or anything
partly made of silver into the bottom of the evaporating dish.
Do not use anything for the appearance of which you care.
Cover the silver with some of the dilute nitric acid, put the
dish over the Bunsen burner on a wire gauze, and bring the
acid to a gentle boil. As soon as it boils, take the dish off,
pour some clean, cold water into it to stop the action, and
pour the liquid off into the clean test tube. Add a few drops
of the dilute hydrochloric acid to the liquid in the test
tube. What happens? What does this show must have been in the
liquid?

You can detect very small amounts of silver in a liquid by this test. It is a regular test in chemical analysis.

THE IODINE TEST FOR STARCH. A very simple test for starch, but one that is thoroughly reliable, is the following:

EXPERIMENT 115. Mix a little starch with water. Add a drop of
iodine. What color does the starch turn? Repeat with sugar.
You can tell what foods have starch in them by testing them
with iodine. If they turn black, blue, or purple instead of
brown, you may be sure there is starch in them. And if they do
not turn black, blue, or purple, you can be equally sure
that they have no starch in them. Some baking powders contain
starch to keep them dry. Test the baking powder in the
laboratory for starch. Often a little cornstarch is mixed
with powdered sugar to keep it from lumping. Test the powdered
sugar in the laboratory to see if it contains starch.

Test the following or any other ten foods to see if any of
them are partly made of starch: salt, potatoes, milk, meat,
sausage, butter, eggs, rice, oatmeal, cornmeal, onions.

THE LIMEWATER TEST FOR CARBON DIOXID. In crowded and badly ventilated rooms carbon dioxid in unusual amounts is in the air. It can be detected by the limewater test.

EXPERIMENT 116. Pour an inch or two of limewater into a
glass. Does it turn milky? Pump ordinary air through it with
a bicycle pump. Now blow air from your lungs through a glass
tube into some fresh limewater until it turns milky. By this
test you can always tell if carbon dioxid (CO_2) is present.

Carbon dioxid turns limewater milky as it combines with the lime in the limewater to make tiny particles (a precipitate) of limestone. If you pour seltzer water or soda pop into limewater, you get the same milkiness, for the bubbles of carbon dioxid in the charged water act as the carbon dioxid in your breath did. If you pumped enough air through the limewater you would produce some milkiness in it, for there is always some carbon dioxid in the air.

The purpose of these experiments is only to give you a general notion of how a chemist analyzes things,--by putting an unknown substance through a series of tests he can tell just what that substance contains; and by accurately weighing and measuring everything he puts in and everything he gets out, he can determine how much of each thing is present in the compound or mixture. To learn to do this accurately takes years of training. But the men who go through this training and analyze substances for us are among the most useful members of the human race.

INFERENCE EXERCISE

Explain the following:

551. A little soda used in canning an acid fruit will save
sugar.

552. The fats you eat are mostly digested in the small
intestine, where there is a large excess of alkali.

553. The dissolved food in the liquid part of the blood gets
out of the blood vessels and in among the cells of the body,
and it is finally taken into the cells through their walls.

554. Ammonia takes the color out of delicate fabrics.

555. Dishes in which cheese has been cooked can be cleaned
quickly by boiling vinegar in them.

556. Prepared pancake flour contains baking powder. It keeps
indefinitely when dry, but if the box gets wet, it spoils.

557. When water or milk is added to prepared pancake flour to
make a batter, bubbles appear all through it.

558. When a roof leaks a _little_, a _large_ spot appears on
the ceiling.

559. Gasoline burns quietly enough in a stove, but if a spark
gets into a can containing gasoline vapor, there is a violent
explosion.

560. Turpentine will remove fresh paint.

GENERAL REVIEW INFERENCE EXERCISE

Explain the following:

561. We can remove fresh stains by pouring boiling water
through them.

562. A ship can be more heavily laden in salt water than in
fresh water.

563. Water flies off a wet dog when he shakes himself.

564. In cooking molasses candy, baking soda is often added to
make it lighter.

565. An egg will not stand on end.

566. Women who carry bundles on their heads stand up very
straight.

567. To get all crayon marks off a blackboard, the janitor
uses _vinegar_ in water.

568. Sunlight makes your skin darker.

569. Water puts out a fire.

570. You get a much worse shock from a live wire when your
hands are wet than when they are dry.

571. Stone or brick buildings are cool in summer but warm in
winter.

572. If you take the handle off a faucet, it is almost
impossible to turn the valve with your fingers.

573. Sparks fly from a grindstone when you are sharpening a
knife.

574. Violin strings are spoiled by getting wet.

575. The oxygen of the air gets into the blood from the lungs,
although there are no holes from the blood vessels into the
lungs.

576. You push a button or turn a key switch and an electric
lamp lights.

577. A rubber comb, rubbed on a piece of wool cloth, will
attract bits of paper to it.

578. People whose eyes no longer adjust themselves have to
have "reading glasses" and "distance glasses" to see clearly.

579. When you look through a triangular glass prism, things
appear to be where they are not.

580. Lye and hot water poured down a clogged kitchen drainpipe
clear out the grease.

581. You can draw on rough paper with charcoal.

582. When little children get new shoes, the soles should be
scratched and made rough.

583. You can get your face very clean by rubbing cold cream
into it, then wiping the cold cream off on a towel or cloth.

584. Soft paper blurs writing when you use ink.

585. Water will flow over the side of a pan through a siphon,
if the outer end of the siphon is lower than the surface of
the water in the pan.

586. There is a loud noise when a gun is fired.

587. Colored cloths should be matched in daylight, not in
artificial light.

588. Lamp chimneys are made of _thin_ glass.

589. When you sweep oiled floors, no dust flies around the
room.

590. The ocean is salty, while lakes are usually fresh.

591. A glass gauge on the side of a water tank shows how high
the Water in the tank is.

592. You burn your hand when you touch a hot stove.

593. Pounding a piece of steel held horizontally over the
earth and pointing north and south will make it become a
magnet.

594. When only one side of a sponge is in water, the sponge
gradually gets soft all over.

595. If we breathe on a cold mirror, a fine mist collects on
it.

596. Butter is kept in cool places.

597. Water will boil more quickly in a covered pan than in an
open one.

598. Mucilage, glue, and paste all become hard and dry after
being spread out on a surface for a while.

599. You cannot see things clearly through a dusty window.

600. In making fire grates it is necessary to have the bars
free to move a little.