308 CHEMISTRY. 



are crystalline solids, some of them with a texture resem- 

 bling organized bodies. And yet this is the case, the word 

 ether having acquired a general meaning, just like oxide. 

 Common ether, then, is oxide of ethyl, the name of the radi- 

 cal C 2 H 5 just mentioned, and its formula is (C 2 H 5 ) 2 O, just 

 like K 2 0, or (NH 4 ) 2 O. 



424. Acids. We will pass over aldehydes and ketones, 

 as they are of no great importance to you. The number 

 of organic acids is enormous. To print their names alone 

 would require many pages* of this book. But it is important 

 to learn their general relations to the preceding bodies. 

 Take the simple example, acetic acid ; analysis shows it to 

 be composed of C 2 H 4 O 2 ; now alcohol is C 2 IT 5 (OH) ; com- 

 pare these two formulae, and you will find one more atom 

 of oxygen in the acid than in the alcohol, and two atoms 

 less of hydrogen. This is the result of substitution, for one 

 O atom, being a dyad, may replace two II atoms, being mo- 

 nads. This is indeed the way acids are regarded; they 

 are derived from their corresponding alcohols by one atom 

 of oxygen replacing two atoms of hydrogen. Let us have 

 recourse once more to graphic formula? : 



Observe that the two atoms of H in the lower left-hand 

 corner of the formula of alcohol disappear in the formula of 

 acetic acid, one atom of O taking their place, and held fast 

 to the carbon by two strokes, signifying its diatomic power. 



