1 8 SCIENCE AND SOIL 



Oxygen and hydrogen are not only very abundant elements 

 (water, the " universal solvent," being H 2 O), but they are also 

 very active, chemically, and one or both have some part in nearly 

 all important groups of compounds. 



Oxids are binary compounds of oxygen with other elements, 

 and they constitute a very large class, because almost all other 

 elements form compounds with oxygen. Important examples 

 are common quartz sand, which is silicon dioxid (SiO 2 ) ; water 

 itself, which is hydrogen oxid (H 2 O) ; and carbon dioxid 

 (CO,). 



Hydroxids are compounds which always contain the radicle 

 OH, which is known as hydroxyl, or the hydroxid group, or the 

 hydroxid radicle. This group, consisting of one atom of oxygen 

 holding one atom of hydrogen with one hand and with the other 

 hand free, or clasping some other atom, is the most important 

 group of atoms in all chemistry. As a group it is monovalent, 

 having one free bond, and it unites with almost all elements. 

 Thus, we may consider: 



Hydrogen hydroxid, HOH, or water. 

 Potassium hydroxid, KOH. 

 Calcium hydroxid, Ca(OH) 2 . 

 Iron hydroxid, Fe(OH) 3 . 

 Silicon hydroxid, Si(OH) 4 . 

 Phosphorus hydroxid, P(OH) 5 . 

 Sulfur hydroxid, S(OH) 6 . 

 Ethyl hydroxid, C 2 H 5 OH, or alcohol. 



In these compounds, the valence of the different elements varies 

 from i to 6, and a corresponding number of hydroxyl groups 

 ( OH) may be held. While these various hydroxids, as KOH, are 

 not strictly binary compounds, the unbroken OH group acts 

 much like an element and the ending -id is used for these com- 

 pounds. This cannot be misunderstood, because potassium hy- 

 droxid (for example) plainly indicates the three elements, potas- 

 sium, hydrogen, and oxygen. 



NOTE. The meanings of a few word endings and prefixes are noted here 

 for reference : 



