=Experiment.=--Take four glass fruit jars, two-quart size, with
straight sides. If you cannot get them with straight sides cut off the
tops with a hot iron just below the shoulder; tin pails will do if the
glass jars cannot be had. Fill these with moist soil from the field or
garden, packing it till it is as hard as the unplowed or unspaded
soil. Leave one of them in this condition; from two of them remove an
inch or two of soil and replace it in the case of one with clean, dry,
coarse sand, and in the case of the other with chaff or straw cut into
half-inch lengths. Stir the soil in the fourth one to a depth of one
inch, leaving it light and crumbly. Now weigh the jars and set them
aside. Weigh each day for several days. The four jars illustrated in
Fig. 30 were prepared in this way and allowed to stand seven days. In
that time they lost the following amounts of water:

Amounts of water lost from jars of prepared soil in seven days.

No. 1 packed soil--lost 5.5 oz. equal to about 75 tons per acre.

No. 2 covered with straw--lost 2 oz. equal to about 27 tons per acre.

No. 3 covered with dry sand--lost 0 oz. equal to about tons per acre.

No. 4 covered with crumbled soil--lost 2.5 oz., equal to about 34 tons
per acre.

Why did not 2, 3 and 4 lose as much water as No. 1?

The soil in jar No. 1 was packed and water was pumped to the surface
by capillary force and was evaporated as fast as it came to the