SUCROSE 



III 



development of the tuber, the following table gives the analysis 

 of samples expressed in percentages of dry matter : — 



In this connection brief allusion may be made to the 

 work of Miller * on sorghum and maize in the leaves of which 

 the maximum of sugars was reached between noon and 5 p.m. 

 after which there was a gradual decrease until dawn. The 

 water-insoluble carbohydrates reached a maximum later than 

 the sugars and a decrease did not begin till about midnight, 

 the minimum being at about dawn. It was also observed that 

 the reducing sugars varied far less than the non-reducing 

 sugars over the twenty-four hours. 



The conclusion drawn by many that sucrose is the first 

 sugar of photosynthesis is a matter of dispute, an aspect 

 of the subject which is considered in the second volume of 

 the present work. 



Preparation. 



The two chief sources for the preparation of cane sugar on 

 a manufacturing scale are the sugar cane and the beet. The 

 processes used in both cases are more or less similar, and con- 

 sist in obtaining, purifying, concentrating and, lastly, crystal- 

 lizing the juice. The juice is generally obtained from the 

 cane by crushing, as much as 85-95 per cent of the juice 

 being expressed in this way ; in some cases it is extracted by 

 diffusion, which consists in immersing the cane in water, when 

 the sugar diffuses out of the cells into the surrounding water 

 while the indiffusible colloids remain behind. The crude juice 

 is then boiled with milk of lime, in order to neutralize any acid 

 present and to precipitate coagulable proteins, and is subse- 

 quently treated with sulphur dioxide. After filtering, the 

 solution is concentrated in a vacuum and allowed to crystallize, 



* Miller : "J, Agric. Res./' 1924, 27, 785. 



