Analysis 373 



The hydrochloric acid test for silver. The experiment 

 in which you tested the action of light in effecting chem- 

 ical change, and in which you made a white powder or 

 precipitate in a silver nitrate solution by adding hydro- 

 chloric acid (page 327), is a regular chemical test to find 

 out whether or not a thing has silver in it. If any silver 

 is dissolved in nitric acid, you will get a precipitate 

 (powder) when hydrochloric acid is added. Make the 

 test in the following experiment : 



Experiment 114. Use distilled water all through this 

 experiment if possible. First wash two test tubes and an 

 evaporating dish thoroughly, rinsing them several times. 

 Into one test tube pour some nitric acid diluted i to 4. Heat 

 this to boiling, then add a few drops of hydrochloric acid 

 diluted i to 10. Does anything happen? Pour out this 

 acid and rinse the dish thoroughly. Now put a piece of 

 silver or anything partly made of silver into the bottom of 

 the evaporating dish. Do not use anything for the appear- 

 ance of which you care. Cover the silver with some of the 

 dilute nitric acid, put the dish over the Bunsen burner on a wire 

 gauze, and bring the acid to a gentle boil. As soon as it 

 boils, take the dish off, pour some clean, cold water into it 

 to stop the action, and pour the liquid off into the clean test 

 tube. Add a few drops of the dilute hydrochloric acid to 

 the liquid in the test tube. What happens? What does 

 this show must have been in the liquid? 



You can detect very small amounts of silver in a liquid 

 by this test. It is a regular test in chemical analysis. 



The iodine test for starch. A very simple test for 

 starch, but one that is thoroughly reliable, is the follow- 

 ing: 



Experiment 115. Mix a little starch with water. Add a 

 drop of iodine. What color does the starch turn? Repeat 



