THE ROOT 77 
THE SOIL. 
The basis of ordinary garden soil, as of most other 
soils, is decomposed, or broken down rock. This forms 
its mineral, or inorganic constituent. Organic material, 
derived from decomposing plant and animal products, 
is also present, forming what is called the humus. 
There is, moreover, a certain amount of water, and, in 
addition, countless myriads of bacteria and moulds that 
are busy breaking up the organic compounds and 
making them ready for green plants. 
To estimate the water, weigh as expeditiously as 
possible a portion of the soil to be investigated, and 
then leave it for several days spread out exposed to the 
air. The loss observed on re-weighing will give the 
weight of water held in the pores between the soil 
erains. A smaller portion of this air-dried soil may now 
be ground fine, weighed, and placed in a drying oven, 
which is kept at a temperature of 100° C. by a jacket 
of boiling water. After some hours re-weigh the soil. 
The loss of weight indicates the moisture held, even in 
the driest weather, as an invisible film on the surface 
of the soil grains. To determine the percentage of 
humus the dry soil derived from the last experiment 
must be burned. It may be mentioned that, in order 
to secure complete combustion, a large blowpipe, or, 
better still, a furnace is required. Owing to lack of 
apparatus the last experiment will doubtless be omitted 
in many cases. 
Mechanical analysis of a soil is a long and tedious 
process but there are rough methods by which general 
structure may be determined. Make or obtain a 
number of small sieves, using wire gauze of the fol- 
lowing meshes :—5 m.m., 3 m.m., 1 m.m., *2 m.m. The 
last mesh is that used for testing the fineness of basic 
slag. Weigh out 100 grams of soil and stir it up with 
water in a glass vessel. Allow it to stand for 10 
