EXTENSION COURSE IN SOILS. 15 
nitrate, a common source of nitrogen, is readily leached from the 
soil. Very little loss occurs from the leaching of phosphorus com- 
pounds. The amount of leaching also varies considerably with the 
type of soil. Soluble materials are leached more readily from sandy 
soils, for example, than from clays. Erosion is another cause of 
much loss of fertility from soils. Leaching and erosion can both 
be avoided to a large extent by keeping the soil covered with plant 
growth. 
There are several ways and means by which plant-food materials 
are replenished in the soil The removal by different agencies of 
surface-soil materials subjects the subsurface to increased action 
from the agencies of disintegration and decomposition which set 
free plant food. Then the dissolving action of water in the soil is 
constantly increasing the availability of the mineral nutrients. The 
return of organic matter in the form of manures, straw, and plant 
residues from crops and weeds is doubtless the best means at the 
command of the average farmer for keeping up the productive- 
ness of his soil. Various substances in the form of commercial ferti- 
lizers are now much used, the quantity and nature of these materials 
depending upon the type of soil, the crops grown, and the judgment 
of the user. 
EXERCISES, LESSON II. 
Materials needed. — Balance; porcelain dishes; sodium hydroxid; red and blue 
litmus paper; muriatic acid; burnt lime; covered fruit jar; glass tubing; one-holed 
stoppers; rubber tubing; limestone; marble slab; some small boxes; sandy soil and 
a few kernels of corn; sealing wax; large-mouthed pickle bottles; and eggs (to be 
furnished by the class). 
Composition of plants. — Take a growing plant and weigh it. Record the weight. 
Cut up and put pieces into a porcelain dish. Heat very gradually, causing the plant 
to wilt and dry out. but do not apply enough heat to cause charring or burning. While 
the drying is being done, hold a clean, dry glass plate over the containing dish. 
Remove glass at times and note from its appearance what is being expelled from the 
plant. After the plant is thoroughly dried, cool and weigh again. Record the 
weight. What percentage of the total weight passed off as moisture? Now burn the 
dried substance until only ash remains. Weigh again. Record the weight and 
figure the percentage of ash. The ash contains the mineral materials taken from the 
soil. The part consumed by burning represents what was formed from the carbon 
dioxid of the air and the water and nitrogen from the soil. 
Formation of a salt. — Dissolve a piece of sodium hydroxid about the size of two 
peas in a small quantity of water. Dip the tips of forefinger and thumb into the solu- 
tion and rub together. Note the feeling, then wash finger and thumb. Put about 
one-fourth teaspoonful of this solution into a separate dish (keeping remainder) and 
add about 5 teaspoonfuls of water. Dip finger into this solution and touch to the 
tongue. Note taste, then spit out. Put small piece of red litmus paper into this 
weak solution. WTiat happens? Sodium hydroxid is a base. After noting all its 
properties, discard this weak solution. 
(a) Put about 10 teaspoonfuls of water into a dish. Add not over 5 drops of muriatic 
acid and stir. Touch tip of finger to solution and taste, but do not swallow. After 
