COMPOSITION OF LIFELESS AND LIVING THINGS 17 



Preparation of Fehling's Solution: To make Fehling's solution 

 dissolve 3 teaspoonfuls (34.64 grams) of pure pulverized copper sul- 

 phate (blue vitriol) in a little less than a half -pint of water (200 cc.). 

 Make a second solution by dissolving in a pint (500 cc.) of water 

 twelve heaping teaspoonfuls (150 grams) of Rochelle salt and 3 (5- 

 inch) sticks of caustic soda (50 grams). Fehling's solution does not 

 keep for any great length of time, and hence must be made up fresh 

 a short time before it is needed. To do this, thoroughly mix two 

 volumes of the copper sulphate solution and five volumes of the 

 solution of Rochelle salt and caustic soda, and dilute the mixture 

 with an equal volume of water. It is more convenient to prepare 

 it in small quantities from the tablets that may be obtained of 

 druggists. Before making any tests boil a small quantity of the 

 Fehling's solution in a clean test tube. If it retains its transparent 

 blue color, it is ready for use; otherwise a fresh supply must be 

 prepared. 1 



1. Dissolve a small amount of grape sugar (glucose) in 



water in a test tube. Add some Fehling's solution and 

 boil. What change in color do you notice? 



2. Try the effect of Fehling's solution on each of the other 



food substances as follows : Put a small amount of starch 

 into a test tube; into a second tube some white of egg; 

 into a third tube some fat or oil; into a fourth tube some 

 mineral matter (salt) ; and into a fifth tube some water. 

 Add a little water to each tube, then pour in a small 

 amount of Fehling's solution and boil as in 1 above. Do 

 any of the colors produced resemble at all the color of 

 the Fehling's solution when it was boiled with grape sugar? 



3. From the preceding experiments state how you can deter- 



mine whether or not a substance contains grape sugar. 



4. (Optional.) Test as many foods as you can (e.g. onions, 

 grapes, pears, granulated sugar, honey, molasses, parsnip, raw 

 meat, milk, egg) in the following manner : Put a small amount 

 of a given food into a test tube, add a little water, and a 



1 From Peabody's " Laboratory Exercises." Henry Holt & Co., 

 New York, 

 c 



