NESSLER PROCESS 481 



Nessler Reagent. Dissolve 35 grams of potassium iodid in 

 100 cubic centimeters of water. Add gradually to this solu- 

 tion, a solution of 17 grams of mercuric chlorid in 300 cubic centi- 

 meters of water until a permanent precipitate of mercuric iodid 

 is formed. Add enough of a 20 per cent, solution of sodium 

 hydroxid to make 1000 cubic centimeters. 



The mixed solutions, at room temperature, are treated with 

 additional mercuric chlorid until the precipitate formed, after 

 thorough stirring, remains undissolved. This precipitate is al- 

 lowed to subside, and when the supernatant liquid is perfectly 

 clear, it is decanted or filtered through asbestos and kept in a 

 well-stoppered bottle in a dark place. The part in use should 

 be transferred to a smaller bottle as required. The solution 

 should be made for a few days before using, since its delicacy is 

 increased by keeping. The nessler reagent should show a faint 

 yellow tint. If colorless it is not delicate, and shows the addi- 

 tion of an insufficient quantity of mercuric chlorid. When 

 properly prepared, two cubic centimeters of the reagent poured 

 into 50 cubic centimeters of water containing 0.05 milligram of 

 ammonia will at once develop a yellowish brown tint. 



Preparation of Ammonia-Free Water. To pure distilled 

 water add pure, recently-ignited sodium carbonate, from one to 

 two grams per liter, and distil. When one-fourth of the whole 

 has passed over, the distillate may be regarded as free from am- 

 monia, and 50 cubic centimeters of the following distillate should 

 give no reaction with the nessler reagent. The distillation is 

 continued until the residual volume in the retort is about one- 

 fourth of the original, and the distillate free of ammonia is care- 

 fully preserved in close glass-stoppered bottles previously washed 

 with ammonia-free water. Pure water, free of ammonia, may 

 also be obtained by distilling with sulfuric acid. 



Comparative Solution of Ammonium Chlorid Containing 

 o.ooooi Gram Ammonia in One Cubic Centimeter. Dissolve 3.15 

 grams H 4 NC1 in ammonia-free water and make the volume up to 

 one liter. Dilute 10 cubic centimeters of the above solution to 

 1000 with water, free from ammonia. 



Solution Containing o.ooooi Gram Nitrogen in One Cubic 

 16 



