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100.

10
Centigrade

HUMIDITY AND HEALTH (II-1)

The problem. The necessity for reliable information about the moisture of the air arises from the fact that this moisture affects health, the drying out of wood and furniture, and the behavior of cloth etc. A damp basement often contributes to the rapid formation of rust and mold. It is probable that the dry air of heated houses is injurious to health. The water vapor actually present in a cubic meter of air is called the absolute humidity. This space may or may not contain all the vapor possible at this temperature.

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If the temperature is sufficiently low, part of the moisture will condense. Relative humidity should vary from 40 to 70 per cent in houses. What is the relative humidity in this room? By relative humidity we mean the percentage of saturation at the given temperature.

What to use. Small baking-powder can, thermometer, ice, beaker or cup, reference table (page 25 of the text) water, salt, and dry towel.

What to do. 1. Assemble the apparatus as shown in figure 10. Fill the can to a depth of about two inches with water. Note the temperature of the room and record in the table below. Put some ice in the water and stir slowly, noting the outside of the can closely for any change. Note the temperature of the water the instant this change appears. Be careful not to break the bulb of the thermometer. Do not allow the moisture from the breath to deposit on the can. If no results are secured when the water is near 0° C. (32° F.) add salt to the water and repeat the process.

2. Dry the outside of the can with a towel and repeat 1. Record all the data in the table below and make the calculations suggested. Refer to page 24 of the text for suggestions.

Questions. What was the room temperature ? At what temperature did the moisture appear? Why is it best to stir the water ?

Suggestions for report. The readings should be recorded as follows:

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As the values are obtained they should be placed upon the blackboard. Take the average as the probable humidity.

Reference work. Read Chapter II of the text.

Optional problem. Refer to the Scientific American, Vol. 115 (September 16, 1916), p. 264, for various forms of hygrometers. Can you make one of these ?

CAUSES OF VARIATION IN ATMOSPHERIC

TEMPERATURE (III-1)

The problem. The change of temperature that comes with the seasons is to many of us the most striking difference between the seasons. Why should there be any difference in temperature? Is the sun giving off as much heat as before ? Are we farther away from the sun ? Why should it make any difference in the heat received by the earth whether the sun is high up in the heavens or lower down near the horizon ?

What to use. Piece of cardboard twelve inches square, tacks, string, and yardstick.

What to do. 1. This experiment should be started a week or more before the date of final observation and discussion. Place a large piece of cardboard with a hole three eighths of an inch in diameter in the upper part of a south window and fasten it securely. Notice the spot of sunlight on the floor at 9 A.M., 12 m., and 3 P.M.

Trace these positions of the spot on the floor and record the date.

2. Note the position of the spot at these hours a week or more later. Note the date and record the positions as before.

Questions. What variations are there in the spot on the floor at different times ? When is it smallest ? largest ? Is there a relation between the area covered by the sunlight and the temperature produced ? Is the spot the same distance from the window at 12 o'clock on successive days ? What does this indicate about the sun's position at noon at different times of the year? Why does the sun have these positions ?

Suggestions for report. Make a drawing showing the conditions on the different dates. Correct answers for the questions above should be written in the notebook.

Reference work. Read Chapter III of the text. Write answers to the questions given on page 32 of the text.

Optional problems. Can you design and construct a simple piece of apparatus by means of which to show the area covered by a beam of light which is a square inch in cross section as it strikes a level surface at 9 A.M., 12 m., and 3 P.M.?

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