FOOD MATERIALS AND HOW TO DETECT THEM 25 



Note. Fehling's Solution. In a bottle labeled " Fehling's 

 Sol. A " put 34.65 grams of cupric sulphate dissolved in 500 cc. of 

 water. 



In another bottle labeled " Fehling's Sol. B " put a solution of 

 125 grams of potassium hydroxide or sodium hydroxide and 173 

 grams of Rochelle salt dissolved in 500 cc. of water. Keep solu- 

 tions " A " and " B " separate until ready for use, then mix equal 

 portions. 



Benedict's Solution. " With the aid of heat dissolve 173 grams 

 sodium citrate and 100 grams sodium carbonate in about 600 cc. 

 water. Filter into a glass graduate and make up to 850 cc. with 

 water. Dissolve 17.3 grams copper sulphate in 100 cc. water and 

 make up to 150 cc. with more water. 



" Pour the carbonate-citrate solution into a large beaker and add 

 the cupric sulphate solution slowly with constant stirring. 



" The mixed solution does not deteriorate on long standing." - 

 Hawk's Practical Physiological Chemistry. 



11. GRAPE SUGAR 



Object. To demonstrate the action of diastase in 

 starch to grape sugar. 



Method. Prepare a small quantity of very dilute 

 starch paste. Add water until there is no appearance of 

 starch, but on testing with iodine solution a clear blue is 

 seen. Fill the test tube f full of the starch. To one add a 

 small quantity of diastase. Put both tubes in a warm place 

 for 24 hours. 



Now test both tubes for starch and for grape sugar. 

 Result? Chew a bit of cracker or bread for three minutes. 

 What change in taste takes place ? 



Note. A substance which like diastase can act upon insoluble 

 substances and change them into different soluble substances is 

 called an enzyme. 



