18 PLANT BIOLOGY 



small spoonful of Fehling's solution, and boil. Before making 

 each test make sure that the test tube is clean. Prepare in 

 your note-book a table like the following, and fill in under 

 each head the names of the foods you have proved to contain 

 or to be without grape sugar. 



25. To test foods for proteins (albuminous or nitrogenous 

 substances). Laboratory Study No. 10. 



Materials : White of egg, corn starch, grape sugar, mutton tallow 

 or other fat, salt, water ; piece of meat, milk ; concentrated nitric 

 acid, ammonia ; test tubes; gas or alcohol lamp. 



1. Pour a little concentrated nitric acid on a piece of hard 



boiled egg in a test tube. 



a. What change in color of the egg do you observe ? 



b. (Optional.) Wash the egg with water, add a little concen- 



trated ammonia, and note result. 



2. Try the effect of nitric acid on each of the other food sub- 



stances as follows: Put a small amount of starch 

 into a test tube; into a second tube some grape 

 sugar; into a third some mutton tallow or other 

 fat ; into a fourth some mineral matter (salt) ; 

 and into a fifth tube some water. Add a little con- 

 centrated nitric acid to each of these foods. Is 

 any color produced like that resulting from adding 

 nitric acid to protein? (In case a liquid is to be 

 tested with nitric acid, the mixture should be boiled 

 before deciding whether protein is present or absent.) 



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



mine whether or not a food contains protein. 



