AMMONIA. 287 



amount of standard solution poured out, and z = the total amount 

 in the cylinder containing the standard solution ; then the weight 



of ammonia in 50 c.c. of the distillate = x X . 



z 



It is very important that the 50 c.c. mark on each Nessler 

 cylinder should be accurately the same height ; unless this is so, 

 the thickness of the layer will not be proportional to the volume. 



Nessler Solution. Dissolve 17-5 grammes of potassium 

 iodide in 100 c.c. of water, next dissolve 15 grammes of mercuric 

 chloride in 300 c.c. of water, and mix the two solutions, wash 

 the heavy precipitate that forms well by decantation, and dissolve 

 it in 17-5 grammes of potassium iodide in 100 c.c. of water, add 

 a few drops of mercuric chloride solution till a red precipitate, 

 insoluble on shaking, is produced, and dilute to about 500 c.c., 

 cooling in ice water, and mix with so much of a 50 per cent, 

 caustic soda solution as is equal to 105 grammes of sodium 

 hydroxide previously diluted with 200 c.c. of water and cooled 

 in ice water. Cool well during mixing, and make up to 1 litre. 

 The solution is left to settle and the clear portion decanted for use. 



Standard Ammonium Chloride Solution. Weigh out 

 0*3146 gramme of pure ammonium chloride, and dissolve in 

 100 c.c. of ammonia-free water, dilute 10 c.c. of this to 1 litre 

 with ammonia-free water for use. 1 c.c. =0-00001 gramme NH 3 . 



Ammonia-free Water. Boil ordinary distilled water in a 

 flask to half its bulk and cool in an atmosphere free from 

 ammonia. 



Nitric Acid. Place about 0-01 gramme of diphenylamine in 

 a porcelain basin, add 1 c.c. pure sulphuric acid, and mix ; run 

 two or three drops of the water down the sides of the basin, so 

 that they will flow over the surface of the acid. In the presence 

 of nitrates a blue colour will be developed. From the amount 

 and depth of coloration produced a rough idea of the amount of 

 nitric acid present can be formed, which will be useful in the 

 quantitative estimation. 



Measure 2 c.c. to 10 c.c. of the water by an exact pipette into 

 a porcelain basin, according to the amount indicated by the 

 diphenylamine test, add 1 c.c. of a 2 per cent, solution of sodium 

 salicylate, and evaporate to dryness on the water-bath ; measure 

 also a known volume, usually 2 c.c. of the standard potassium 

 nitrate solution into a porcelain basin, add 1 c.c. of a 2 per cent, 

 solution of sodium salicylate and so much sodium chloride solution 

 as will give an amount of chlorine equal to that in the amount 

 of water taken, and evaporate to dryness. To each add 1 c.c. 

 of sulphuric acid, and heat for five minutes on the water-bath. 

 Dilute to about 20 c.c. with distilled water, make alkaline with 

 caustic soda solution (30 per cent.), and dilute to 50 c.c. Compare 



