ut different kinds of coloring
matter dissolved in them when they were melted.

Many articles are much used chiefly because they are good
_emulsifiers_ or good _solvents_ (dissolve things well). Soap is a
first-rate emulsifier; water is the best solvent in the world; but it
will not dissolve oil and gummy things sufficiently to be of use when
we want them dissolved. Turpentine, alcohol, and gasoline find one of
their chief uses as solvents for gums and oils. Almost all cleaning is
simply a process of dissolving or emulsifying the dirt you want to get
rid of, and washing it away with the liquid. Do not forget that heat
helps to dissolve most things.

_APPLICATION 63._ Explain why clothes are washed in hot suds;
why sugar disappears in hot coffee or tea; why it does not
disappear as quickly in cold lemonade; why you cannot see
through milk as you can through water.

INFERENCE EXERCISE

Explain the following:

381. A kind of lamp bracket is made with a rubber cup. When
you press this cup against the wall or against a piece of
furniture and exhaust the air from the cup, the cup sticks
fast to the wall and supports the lamp bracket.

382. You can take a vaseline stain out with kerosene.

383. If the two poles of an electric battery are connected
with a copper wire, the battery soon becomes discharged.

384. Electric bells have iron bars wound around and around
with insulated copper wire.

385. Piano keys may be cleaned with alcohol.

386. Linemen working with live wires wear heavy rubber gloves.

387. Crayon will not write on the smooth, glazed parts of a
blackboard.

388. Varnish and shellac may be thinned with alcohol.

389. Filtering will take mud out of water, but it will not
remove salt.

390. Explain why only one wire is needed to telegraph between
two stations.

SECTION 42. _Crystals._

How is rock candy made?

Why is there sugar around the mouth of a syrup jug?

How are jewels formed in the earth?

You can learn how crystals are formed--and many gems and rock candy
and the sugar on a syrup jug are all crystals--by making some. Try
this experiment:

EXPERIMENT 83. Fill a test tube one fourth full of powdered
alum; cover the alum with boiling water; hold the tube over
a flame so that the mixture will boil gently; and slowly add
boiling-hot water until all of the alum is