HUMAN STRUCTURE AND LIFE-ACTIVITIES 461 



Into another test-tube. put some Fehling's reagent,* the ingredients 

 of which are usually kept in separate bottles and mixed when needed. 

 Heat the Fehling's reagent, and then with a pipette slowly drop 

 into it some of the sugar solution obtained from the dry fruits ; or 

 drop some of the reagent into the sugar solution. A red color indi- 

 cates the presence of one kind of sugar. One such experiment 

 could not prove that when Fehling's reagent causes a red color it 

 means that sugar is present, for we have not yet tried this solution 

 on starch, fat, and other things. However, chemists have tried the 

 Fehling's reagent on all the substances commonly found in animals 

 and plants, and it has been demonstrated that only certain kinds of 

 sugars produce the red color. We have not time to repeat such 

 inves igations, and so we must accept the chemists' statement that 

 Fehling's reagent is a test for a sugar found in grapes and known as 

 grape-sugar or dextrose. The same sugar in corn-syrup is popularly 

 called glucose. Its chemical formula is CeH^Oe. Ordinary sugars 

 sold in stores are chiefly cane-sugar (CizHaaOn) . Milk-sugar (lactose) 

 and malt-sugar (maltose) have the same chemical formulas as cane- 

 sugar (sucrose). 



Kinds of Sugars. (D or L) Dissolve some commercial glucose, 

 or corn-syrup, in water and test with Fehling's reagent. Dissolve 

 some ordinary "granulated" sugar in water, and test. This latter 

 will sometimes give no red color until after it has been boiled for some 

 time or treated with strong acids. The explanation is that most 

 "granulated" sugar is chiefly the kind known as cane-sugar, while 

 sugars which give red color in Fehling's test are of the kinds known as 

 grape-sugar and fruit-sugar. The boiling or treating with acid 

 changes the cane-sugar into the other kinds ; and these can then be 

 tested with Fehling's reagent. Taste granulated sugar and glucose, 

 and compare as to sweetness. As a practical point, it is interesting 

 to note that granulated sugar should be added to fruits after cooking. 

 If added before, the sweetness will be partly lost by change to the 

 other sugars, which are as good food, but less sweet. 



Tests for Fat. (D or L) Put a drop of olive oil on a sheet of white 

 paper, and note that a grease-spot is produced. Dissolve some beef- 

 suet in a small quantity of benzine or ether (keep such volatile 

 liquids as these far away from a flame), put a drop of the solution on 

 paper, and notice the spot left after evaporation of the benzine. 



* Fehling's reagent, a test for certain kinds of sugar, may be purchased 

 from dealers in chemicals or at ordinary drug-stores. It may be made ac- 

 cording to the formula in the "Teachers' Manual" which accompanies this 

 book. 



