ELEMENTAEY COUESE 



LESSON I 

 THE CABBOHYDRATES AND FATS 



1. Note the general appearance of the specimens of grape sugar or dex- 

 trose, cane sugar, dextrin, and starch which are given round, 



2. Put some of each into cold water. Starch is insoluble ; dextrose, cane 

 sugar, and dextrin dissolve after a time, but more readily in hot water. 



3. Trommer's test for dextrose. — Put a few drops of copper sulphate solu- 

 tion into a test-tube, then solution of dextrose, and then strong caustic potash. 

 On adding the caustic potash a precipitate is first formed, which, owing to 

 the presence of the sugar, rapidly redissolves, forming a blue solution. On 

 boUiug this a yeUow or red precipitate (cuprous hydrate or oxide) forms. 



Fehling's test for dextrose. — Fehling's solution is a mixture of copper 

 sulphate, caustic soda, and Eochelle salt of a certain strength. It is used for 

 estimating dextrose quantitatively (see Lesson XII.). It may be used «ks a 

 qualitative test also. Boil some Fehling's solution ; if it remains clear iti? 

 in good condition ; add to it an equal volume of solution of dextrose and boil 

 again. Reduction, resvdting in the formation of cuprous hydrate or oxide, 

 takes place as in Trommer's test. 



4. Canr Sugar. — (a) The solution of cane sugar when mixed with copper 

 sulphate and caustic potash gives a blue solution. But on boiling no reduc- 

 tion occurs. 



(6) Take some of the cane sugar solution and boil it with a few drops of 

 25-per-cent. sulphuric acid. This converts it into equal parts of 

 dextrose and le\iilose. It then gives Trommer's or Fehling's test 

 in the typical way. 



(c) BoU some of the cane sugar solution with an equal volume of con- 

 centrated hydrochloric acid. A deep red solution is formed. Dex- 

 trose, lactose, and maltose do not give this test. 



5. Starch. — (a) Examine microscopically the scrapings from the surface 

 of a freshly cut potato. Note the appearance of the starch grains with their 

 concentric marlongs. 



(6) On boiling starch with water an opalescent solution is formed, 

 which, if strong, gelatinises on cooling. 



(c) Add iodine solution. An intense blue colour is produced, which dis- 



appears on heating, and if not heated too long reappears on cooling. 

 N.B. — Prolonged heating drives off the iodine, and consequently 

 no blue colour returns after cooling. 



(d) Conversion into dextrin and dextrose. To some starch solution in a 



flask add a few drops of 25-per-cent. sulphuric acid, and boil for 

 15 minutes. Take some of the hquid, which is now clear, and show 

 the presence of dextrin and dextrose. 



