196 ACIDS, ALKALIES, AND CLEANING 



with a few drops of concentrated nitric acid, and boiled for a few 

 minutes. Then a few drops of a solution of potassium thiocyanate or 

 ammonium thiocyanate are added. A blood-red solution results; this 

 is pink if only a little iron is present. 



7. Sodium Salts are tested for by the bright, yellow flame they give 

 when they are held, on a platinum wire, in the colorless gas flame (cf. 

 240). 



8. Potassium Salts give a violet color to the colorless gas flame. The 

 color is seen best when it is viewed through blue glass; this cuts off the 

 yellow rays of sodium. 



9. Calcium Salts. We test for a calcium salt by treating its solu- 

 tion with ammonia water and a solution of ammonium oxalate (the 

 ammonium salt of oxalic acid). A white precipitate of calcium oxalate 

 is formed. We pour off the liquid portion from the precipitate, and 

 add dilute acetic acid to the precipitate. If the precipitate is really 

 calcium oxalate, it will not be dissolved. 



10. Ammonium Salts. We test for ammonium salts by adding 

 them, in solution, to a small lump of quicklime, or about 5 c.c. of sodium 

 hydroxide solution, and warming the mixture gently. Ammonia is 

 given off, and can be known by its odor. 



222. Exercises. 



1. Why do we add soda to tomatoes in making " cream tomato" 

 soup? How do sour milk and soda "raise" biscuits? Why do straw- 

 berries curdle milk? 



2. How could you tell whether a soil was "sour" or not? 



3. Lime water is often added to milk before the milk is given to a 

 child or an invalid; why? 



4. " Galvanized iron " is iron covered with zinc. Is it a safe material 

 for utensils in which fruits are cooked? Why? Is "tinned" iron 

 safer? Why? 



5. What base would you use if you wished to make some potassium 

 nitrate by neutralization? What acid would you use? How would 

 you tell when you had just the right amount of each? 



6. In moist weather, laboratory bottles sometimes lose their labels. 

 If this occurred, how could you tell whether a certain solid was, or was 



