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 dissolved. Do not add any more water than you have to, and keep stirring the alum with a glass rod while you are adding the water. Pour half of the solution into another test tube for the next experiment. Hang a string in the first test tube so that it touches the bottom of the tube. Set it aside to cool, uncovered. The next day examine the string and the bottom of the tube.
Experiment 84. While the solution of alum in the second test tube (Experiment 83) is still hot, hold the tube in a pan of cold water and shake or stir it until it cools. When white specks appear in the clear solution, pour off as much of the clear part of the liquid as you can; then pour a little of the rest on a glass slide, and examine the specks under a microscope.
