III.] THE CARBOHYDRATES. 2 5 



and the solution contains a mixture of dextrose and laevulose. 

 Test its reducing power with Fehling's solution. 



Cane-Sugar. Water. Glucose. Laeyulosa 



^12^22^11 + ^2^ = ^6^12^6 + ^0^12^6' 



(h.) Estimation of Cane-Sugar. — Take lo cc. of the cane-sugar 

 solution, add i cc. of a 25 per cent, solution of H2SO4. Boil for 

 half an hour, and then make up bulk of fluid to its original 

 volume. The cane-sugar is converted into a reducing sugar, 

 dextrose. Place tlie fluid in a burette, and estimate its reducing 

 power on Fehling's solution (see "Urine.") 95 parts of glucose 

 correspond to 100 parts of cane-sugar. 



15. Invert Sugar — a mixture of grape-sugar and fruit-sugar— is widely 

 distributed throughout the vegetable kingdom, and is so called because it 

 rotates the plane of polarised light to the left, the specific rotatory power of 

 the laevulose being greater than that of dextrose at ordinary temperatures. 



16. Conversion of Starch into a Eeducing Sugar. — Place 50 

 cc. of starch solution in a flask on wire gauze over a Bunsen burner, 

 add one drop of strong sulphuric acid, and boil from five to ten 

 minutes, observing the spluttering that occurs, the liquid meantime 

 becoming clear and limpid. 



{a.) Test a portion of the liquid for glucose, taking care that 

 sufficient alkali is added to neutralise the surplus acid. 



(h.) Add iodine = blue colour, showing that some soluble starch 

 (amidulin) remains unconverted into a reducing sugar. 



ADDITIONAL EXERCISES. 

 Polarimeters, 



17. Circumpolarisation.— Certain substances when dissolved possess the 

 power of rotating the plane of polarised light, e.g., the proteids, sugars, &c. 

 The extent of the rotation depends on the. amount of the active substance 

 in solution. The direction of rotation— ?.c., to the right or the left —is 

 constant for each active substance. Of course, light of the same wave- 

 length must be used. The light obtained from the volatilisation of common 

 salt is used. 



The term "specific rotatory power," or "specific rotation" of a substance, 

 is used to indicate the amount of rotation expressed in degrees of the plane of 

 polarised light which is produced by i gram of the substance dissolved in 

 I cc. of liquid, when examined in a layer i decimetre thick. 



Those substances which cause specific rotation are spoken of as ' * optically 

 active ;" those which do not, as '* inactive." 



