Take two dishes—plates or saucers—exactly alike. Have one clean and the other soiled with butter or some well-known substance. Ask the class the difference between them. One is clean and one dirty. What substance is on one that hinders your saying it is clean? Butter. What else could be on it? Jam. What else? Dust. What else? Gravy. Now instead of telling the name of the particular substance in each case, let us try to find one name that will apply to all of the substances which, as you say, make the dish dirty. Let us give these substances a name which will show that they do not belong to the plate. We may call each of them a foreign substance. And if I take the substance off the plate what am I doing to the plate? Cleaning it. Then what is cleaning? Cleaning is removing a foreign substance.
METHODS OF CLEANING
1. Scraping or rubbing away the foreign substance:
What would you use to remove the butter from the plate? A piece of paper or a knife. What are you doing with the knife or paper? Scraping or rubbing off the foreign substance. Then how was it removed? It was removed by scraping or rubbing.
Suppose some one has sharpened a pencil and let the pieces fall on the floor, what would you take to remove the foreign substance from the floor? A broom. What would you say you are doing with the broom? Sweeping. How does the movement of the broom over the floor compare with the movement of the knife over the plate? It is similar. What would you take to remove the dust from the window-sill? A duster. What would you say you are doing? Dusting. How does the movement of the duster compare with the movement of the knife and the broom? It is similar. In all of these cases of dish, floor, and sill, how did we remove the foreign substance? We scraped or rubbed it off. Name one way of removing a foreign substance. Scraping or rubbing it away.
2. Dissolving the foreign substance and then scraping it away:
Show a much soiled towel and ask what is usually done to clean it. It is washed. Ask the pupils to tell just what they mean by that. The towel is put in water and soap used on it. What effect will the soap and water have on the foreign substance? They will soften or dissolve it. Then what must be done next? The towel must be rubbed on a board or with the hands. What effect has this operation on the foreign substance? It scrapes or rubs the foreign substance away. Then we have another way of cleaning: By first dissolving the foreign substance, and then scraping or rubbing it away.
A number of well-known cleaning operations may then be given, and the pupils asked in each case to decide the method used—such as, whisking a coat, scrubbing a table, cleaning the teeth, or washing dishes.
COMMON HOUSEHOLD CLEANSING AGENTS
Next, get lists of the common cleansing agents found in an ordinary home, and arrange them in order of coarseness.