SUGAR 421 



melting-point ascertained. The osazone is represented by the 

 following formula : 



CH 2 -OH 



I ' 

 CH-OH 



CH-OH 



CH-OH 



C : N-NHC 6 H 5 



CH : N-NHC 6 H 5 



Fructose undergoes exactly similar changes and yields an 

 osazone identical with the compound obtained from glucose. 

 The osazones when heated with a little hydrochloric acid give up 

 their phenylhydrazine, and the resulting compound (called an 

 osone) by the action of zinc dust and glacial acetic acid, takes 

 up two atoms of hydrogen and is converted back into a sac- 

 charose. When the original sugar, like glucose, belonged to the 

 aldehyde type of sugar, the product of this change will be a 

 sugar of the keto type ; if, for example, the process starts with 

 glucose the decomposition product of the osazone will be fruc- 

 tose. 



These saccharoses are readily convertible the one into the other, 

 sometimes by mere dissolution in a neutral solvent like water, 

 or by prolonged contact with solutions of ammonia or other 

 alkali. Ordinary glucose, for example, when freshly dissolved 

 in water rotates the plane of polarisation to the right, and its 

 specific rotatory power is represented by 105-2, but if kept for 

 a few hours this falls to 52- 6. This change is attributed to the 

 formation of an equilibrium mixture of three isomeric forms of 

 glucose. 



The methods by which the synthesis of the natural sugars, as 

 well as of others, containing respectively less or more carbon in 

 the fundamental chain can only be indicated by one or two 

 examples. Of these the most interesting perhaps are those 

 which start from very simple compounds, the synthetical forma- 

 tion of which was long ago established. 



The first case which naturally presents itself is the sugar which 



