THE ELEMENTS IN NATURE 25 



Sulfur S. 



Tantalum Ta. 



Tellurium Te. 



Terbium Tb. 



Thallium Tl. 



Thorium Th. 



Thulium Tm. 



Tin Sn. 



Titanium Ti. 



Tungsten W. 



Uranium U. 



Vanadium V. 



Xenon Xe. 



Ytterbium Yb. 



Yttrium Y. 



Zinc Zn. 



Zirconium Zr. 



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 2.32 



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, potassiimi, phosphorus, iron, sulfur, 

 from the soil; carbon, hydrogen, oxygen, nitrogen, from tha atmos- 

 phere. Combinations formed by the vital processes of plants and 

 animals — as starch, sugar, acetic acid — are known as organic com- 

 pounds; 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, car- 

 bon, and hydrogen. The younger and more succulent the plant, the 



