AGRICULTURAL ANALYSIS 



Preparation of the Nessler Solution. Sixteen grams of mer- 

 curic chlorid are dissolved in about one-half liter of pure water 

 and 35 grams of potassium iodid in about 200 cubic centimeters 

 of pure water and the first solution is poured slowly into the 

 second until a slight excess is indicated by the appearance of a 

 color or a precipitate. To the mixture are added 160 grams of 

 solid potassium hydrate, and when this is dissolved, the volume is 

 made up to one liter. A strong solution of mercuric chlorid is 

 added little by little until the red mercuric iodid which is formed 

 is not redissolved. The precipitate should not be removed by 

 filtration but allowed to subside, and the completed reagent 

 shows a pale straw color. The reaction which takes place in 

 the presence of ammonia is represented as follows : 



(22KI, HgI 2 )+NH 8 +3KOH=NHgJH 2 O+7KI+2H 2 O. 



Pure Water. Mason prepares pure water in a live gallon cop- 

 per retort using good spring water which is treated with a 

 few crystals of potassium permanganate and subjected to dis- 

 tillation until 50 cubic centimeters when nesslerized give no 

 brown color in 10 minutes. The distillation should not be push- 

 ed too far otherwise ammonia may be generated from any or- 

 ganic matter which may be present in the water. 



413. Nessler Reagent of Ilosvay. To secure greater delicacy 

 in nesslerizing, Ilosvay uses a reagent prepared as follows : 97 



Dissolve two grams of potassium iodid in five cubic centi- 

 meters of water, heat the solution gently, and add three grams 

 of mercuric iodid. After the solution is cooled, add another 

 portion of three grams of the mercury salt, and then 20 

 cubic centimeters of water, and wait until the precipitation is 

 complete. After filtering, there are added to the filtrate from 20 

 to 30 cubic centimeters of a 20 per cent, solution of potassium 

 hydroxid. Only the limpid supernatant liquid is used in the 

 analytical work. With this reagent, Ilosvay has been able to de- 

 tect 0.02 milligram of ammonia in 1 10 cubic centimeters of water. 



97 Bulletin de la Socite chimique de Paris, 1894, [3], 11 : 216. 



