154 CHEMISTR V FOR A GRICUL TURAL STUDENTS 



Oxidation of alcohols proceeds in two stages. Two atoms of hydrogen 

 are first withdrawn, and an aldehyde {i.e. alcohol dehydxogQn3i\Mm) left, and 

 then an atom of oxygen is introduced and an acid formed. Formic alde- 

 hyde, CHgO, intermediate between methyl alcohol and formic acid, is the 

 useful antiseptic and preservative, the solution of which is known in com- 

 merce as "formalin." Benzoic aldehyde, CyllgO, constitutes the volatile 

 oil of bitter almonds. It should be noted that oxidation does not always 

 imply addition of oxygen to the substance. The withdrawal of hydrogen, 

 with formation of water, is also held to be a process of oxidation. Con- 

 versely, reduction may imply either elimination of oxygen or addition of 

 hydrogen. 



By oxidising monohydric alcohols, monobasic acids, i.e. 

 acids containing only one atom of hydrogen replaceable by 

 metals, are obtained, but polyhydric alcohols can yield poly- 

 basic acids, i.e. acids containing two or more replaceable hydro- 

 gens. To show the basicity of the acids, it is convenient to 

 represent them by formulae in which the replaceable hydrogen 

 precedes the remainder of the formula. 



Formic acid, HCHO2, occurs in ants and nettles. 



Acetic acid, HC2H3O2, ,, vinegar and pyroligneous acid. 



Lactic acid, HC3H5O3, , , sour milk. 



Butyric acid, HC4H7O2, ,, cream and butter as butyrate of glyceryl. 



Myristic acid, HC14H27O2, ,, cream and butter as myristate of glyceryl. 



Palmitic acid, HC16H31O2, ,, palm oil and soft fats as palmitate of 



glyceryl. 

 Stearic acid, HC18H35O2, ,, hard fats as stearate of glyceryl. 

 Oleic acid, HC18H33O2, ,, olive oil and soft fats as oleate of 



glyceryl. 

 Benzoic acid, HC7H5O2, ,, gum benzoin. 

 Salicylic acid, HC7H5O3, ,, oil of wintergreen as salicylate of 



methyl. 

 Oxalic acid, H2C2O4, ,, sorrel as acid oxalate of potassium (salts 



of sorrel). 

 Tartaric acid, Y{2C4^^0^^, ,, grape juice as acid tartrate of potassium 



(cream of tartar). 

 Citric acid, HgCgHgO;, ,, lime and lemon juice. 



According to the formula given, oxalic acid is a di-basic 

 acid. To confirm this, prepare a deci-normal solution, i.e. a 



