The mass of the earth (and the atmosphere) is at present assumed to be composed of certain elementary or indivisible substances, and of combinations of these substances. The number of elements now recognized by chemists is eighty-three. The names of these elements, with the symbols that are used for convenience and brevity in expressing the combinations into which they unite, are given in the table: —

The elements and their symbols

Chapter II The Elements and the Soil 7

Sulfur.........

S.

Tungsten........

W.

Tantalum........

Ta.

Uranium..........................

U.

Tellurium........

Te.

Vanadium

V.

Terbium........

Tb.

Xenon..........

Xe.

Thallium........

Tl.

Ytterbium..............

Yb.

Thorium........

Th.

Yttrium..................

Y.

Thulium........

Tm.

Zinc...........

Zn.

Tin..........

Sn.

Zirconium...........

Zr.

Titanium........

Ti.

   

Distribution of the Elements

Oxygen, hydrogen, nitrogen, and some of the rarer elements exist in the atmosphere in a pure or free state as well as in combinations in animal and plant and earthy substances; but most of the elements are present in nature only in combination with other elements. The larger number of the eighty-three known elements are very rare. Nearly 99 per cent of the earth's crust (including the water) is made up of eight elements, as follows (according to Clark): —

Oxygen.....

47.02

Silicon......

28.06

Aluminum.................

8.16

Iron.......................

4.64

Calcium......................

3.50

Sodium......................

2.63

Magnesium..................

2.62

Potassium...............................

232

No other element is estimated to contribute as much as 1 per cent to the composition of the crust of the globe. Hydrogen is estimated to comprise .17 per cent, and carbon .12.

The atmosphere is a mixture (by volume) of seventy-nine parts of nitrogen and twenty-one parts of oxygen, with small quantities of argon, carbon dioxid, vapor of water, ammonia, and organic gases in addition.

The elements essential to the life and growth of plants, so far as known, are ten: calcium, magnesium, potassium, phosphorus, iron, sulfur, from the soil; carbon, hydrogen, oxygen, nitrogen, from the atmosphere. Combinations formed by the vital processes of plants and animals — as starch, sugar, acetic acid — are known as organic compounds; all others are inorganic compounds. The different elements making up a compound are calculated in terms of their atomic weights.

The elements of which plants are composed, are largely oxygen, carbon, and hydrogen. The younger and more succulent the plant, the greater the proportion of oxygen and hydrogen, because the proportion of water is greater.

Ultimate composition of a wheat plant at maturity, containing 10 per cent moisture. The hydrogen and oxygen of the water are included in the statement

Carbon.......................

42.87

Hydrogen....................

6.04

Oxygen..........................

45.26

Nitrogen...........................

0.94

Potassium.......................

0.36

Calcium........................

0.33

Phosphorus..............................

0.11

Other ash constituents...........................

4.09

 

100.00

Ultimate composition of human body. The proportion of C varies greatly with the amount of fat, also the O and ash to a less extent. The statement includes the oxygen and hydrogen of the water

Chapter II The Elements and the Soil 8

The water is about 65 per cent, which makes the dry-matter in the animal much less than in the mature plant, the moisture content of which is shown to be 10 per cent in the preceding table.

The Ash and Mineral Parts of Animals and Plants

When a plant is oven-dried, the free or uncombined water passes off. When it is completely burned, the carbon, hydrogen, nitrogen and most of the oxygen are driven off. What remains is ash, containing the mineral elements. Incomplete burning of plant material results in coals and ash; the coal is mostly carbon. Charcoal is carbon.

Composition Of Animals And Man

Mineral elements in animal bodies (Calculated from Results of Lawes and Gilbert)

Composition Of Animals And Man 9

Composition of ash of human body (Beaunis)

Composition Of Animals And Man 10

Composition of the ash of leading farm crops (Snyder)

Composition Of Animals And Man 11