SUGAR. 39 



solution produce a rotation of loo degrees on the 

 per cent, scale, 61.68 grams (20.56 x 3) may be 

 weighted out directly for the purpose and made 

 up to 100 c. c. plus the volume occupied by the 

 fat and proteids, the latter being calculated as above. 

 The sugar containing liquid will then be exactly 

 100 c. c, and the reading on the polarimeter divided 

 by three will give the percentage of hydrated milk 

 sugar direct, if a 200 mm. tube be employed. With 

 a 400 mm. tube or 500 mm. tube the reading is 

 to be divided by 6 or 7.5 respectively. 



Polarimeters. — A discussion of the construction of 

 the various forms of polarimeters and of the optical 

 principles involved, would be beyond the scope of this 

 work. It may be stated that the so called half-shadow 

 instruments, for use with the sodium flame, are the 

 most satisfactory. They are so arranged, by the use 

 of a semicircle of thin quartz, that the field is divided 

 into semicircles which are equally illuminated when 

 the instrument registers zero. On the introduction 

 of the tube carrying the sugar solution, the illumina- 

 tion becomes unequal and the angular rotation of the 

 analyser which is required to restore the original con- 

 dition, measures the rotation which has been caused 

 by the sugar. Most instruments are furnished with 

 two scales, one showing the rotation in angular de- 

 grees and the other expressing per cent, directly. 

 The latter reads to 100 when a certain fixed quantity 

 of the material has been dissolved in water and 

 diluted to 100 c. c. 



