REAGENTS AND QUALITATIVE METHODS 135 



4. One c.c. of chemically pure ammonia is added to each 

 weighing bottle to neutralize the sulphuric acid. 



5. The water and excess of ammonia is then evaporated 

 in an oven at 100 C. and the ammonium sulphate remains 

 behind. If the chemicals are pure, 1000 c.c. of the solution 

 should give 49 grams of sulphuric acid. In 10 c.c. of the 

 solution there should be 0.49 gram of H 2 SO 4 . 



H 2 S0 4 : (NH 4 ) 2 SO 4 :: 98 : 132 

 49 : x :: 98 : 132 

 x = 0.66 



If the solution is exactly normal, there should be 0.6600 

 gram of (NH^SC^ formed from 10 c.c. In case the amount 

 of (NH 4 ) 2 SO4 formed is too great, its factor is determined 

 by dividing 0.6600 into the weight of ammonium sulphate 

 found. If, for instance, the weight of ammonium sulphate 

 is 0.6675, the factor of the solution is 1.0113 + . This 

 means that 10 c.c. of the solution is equivalent to 10.113 c - c - 

 of normal solution. 



(6) Nessler's Reagent for Ammonia: 



1. Dissolve 50 grams of potassium iodid in a small 

 quantity of cold distilled water. 



2. Add a saturated solution of mercuric chlorid until a 

 slight precipitate persists. 



3. Now add 400 c.c. of a 50 per cent, solution of potassium 

 hydroxid made by dissolving the potassium hydroxid and 

 allowing it to clarify by sedimentation before using. 



4. Dilute to 1000 c.c., allow to settle for one week, and 

 decant. This solution gives the required color with am- 

 monia within five minutes after addition. 



5. Keep the Nessler's solution in a well-stoppered bottle 

 away from the light. 



