70 Biological Chemistry. 



sible to ascertain whether it is an alcohol. The essential 

 point is that it should contain the alcoholic hydroxyl 

 group. This should be replaceable by chlorine or bromine 

 when the substance is treated with the pentachloride or 

 pentabromide of phosphorus ; one hydrogen atom, further- 

 more, should be replaceable by sodium, when the substance 

 is treated with this metal. It is also possible to ascertain 

 whether an alcohol is primary, secondary, or tertiary. 

 When a primary alcohol is oxidized under certain con- 

 ditions it yields a substance known as an aldehyde, which, 

 on further oxidation, gives an acid containing the same 

 number of carbon atoms. If the general formula given i 

 above is employed, the formula of the substances produced 

 may be represented thus 



R-CH a OH R CHO R-C0 2 H 



Alcohol. Aldehyde. Acid. 



Or, taking a concrete instance 



CH 3 CH a OH CH 3 -CHO CH 3 C0 2 H 



Ethyl alcohol. Acetaldehyde. Acetic acid. 



This series of reactions always takes place when a sub- 

 stance contains the group CH 2 OH, whatever R may be. 

 Secondary alcohols, on the other hand, yield on oxidation 

 a substance with the same number of carbon atoms known 

 as a ketone, which, on further oxidation, gives a mixture 

 of acids containing a smaller number of carbon atoms than 

 the alcohol ketone. The oxidation to ketones may be 

 represented by the formula 



"R "R 



\PTT VTT ' \r)Q acids with smaller numbers 



TW/ ' ~*T// ~ of carbon atoms. 



K' s\ / 



Conversely, aldehydes and ketones can be converted by 

 nascent hydrogen into primary and secondary alcohols. 

 The chemistry of these important classes of compounds, 



