4 SCIENCE AND SOIL 



an atom of carbon is 12 times, of oxygen is 16 times, of sulfur is 32 

 times, and of chlorin is 35.5 times, as great as the weight of an atom 

 of hydrogen. Thus the atomic weights of all other elements are 

 referred to the weight of the hydrogen atom as the chemical unit. 



Molecules. A molecule is the smallest enduring particle of an 

 element or compound. The atom, if set free, instantly unites with 

 another atom (either of the same element or of a different element) 

 to form a molecule, and the molecule may endure permanently. 

 One atom of hydrogen and one atom of chlorin unite to form one 

 molecule of hydrochloric acid, HC1. The molecular weight of this 

 compound 1536.5, which is the sum of the atomic weights, the weight 

 of the hydrogen atom always being i. It is true that this is an 

 arbitrary standard, but so is every common standard of weight 

 or measure, such as the ounce or the inch or the dollar. The inch 

 is an arbitrary standard of length to which we may refer other 

 lengths or distances, and likewise the weight of the hydrogen atom 

 is an arbitrary standard to which we may with equal accuracy 

 refer the weights of the atoms of all other elements, and also the 

 weights of all molecules of either compounds or elements. 



Atomic bonds. Atomic bonds are the links of union between 

 atoms. This bond between atoms may be likened to the hand clasp 

 between persons, except that under normal conditions the hand of 

 one atom always grasps the hand of another atom. If the bond is 

 broken, the freed hands immediately grasp other hands, breaking 

 the bonds between other atoms if necessary to secure union. At 

 the instant a bond is broken, when free hands exist, the atoms are 

 called nascent, and in that condition they have unusual power to 

 attack the molecules of other elements or compounds. Free 

 hydrogen means hydrogen not combined with some other element. 

 Thus we have nascent hydrogen (H), ordinary free hydrogen 

 (H 2 ), and- combined hydrogen, as in water (H 2 O). Of course, 

 nascent hydrogen is also free hydrogen, but in an extraordinary 

 form; namely, as a free atom, which as such can exist but an 

 instant until it unites with another atom of hydrogen (or of some 

 other element) to form a molecule. 



Valence. Valence refers to the number of bonds, or hands, pos- 

 sessed by an atom. The hydrogen atom has but one hand (H ) , 

 while the oxygen atom has two hands ( O ), and the carbon 



