47 
showing the presence of water; it would blacken and catch flame, 
showing the presence of carbon and other matters dissipated on 
burning ; and there would be left behind a quantity of matter, 
namely, the ash, which would not be dissipated by burning. But 
we should observe an obvious difference between the plants and 
the soil, for whereas in the plants the greater proportion consisted 
of water and the least proportion was the ash or earthy substance ; 
in the soil it is the other way about, the ash or earthy substance 
greatly preponderating. We shall, in fact, find an average soil 
to contain something like the following :— 
AVERAGE COMPOSITION OF SOILS. 
Parts in 100,000. 
Water wis rae swe ... 10,000 
Burnable matter, commonly called humus... 8,000 
(Consisting of carbon, the elements 
of water, and nitrogen, the nitro- 
gen amounting to saa at 200) 
Earthy substance or ash, consisting of— 
Alumina a wi -» » 1,000 
Oxide of iron... ON 3,500 
Lime oy site “eee B50 
Magnesia side ba i 250 
Potash wee use ait 200 
Soda avi van iets 150 
Phosphoric acid aes eee 100 
Sulphuric acid ... ees oe 150 
Chlorine — sass es 10 
Carbonic acid ... ies ae 300 
Soluble silica ... aed a8 250 
Insoluble silica and sand ... 75,740 ‘ 
82,000 
100,000 
From this list we see that there is everything in the soil that 
there is in the plant. Yet we may not from this fact conclude 
