WATER ANALYSIS. 287 



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 35 grammes of potassium iodide 

 in 100 c.c. of water ; next dissolve 17 grammes of mercuric 

 chloride in 300 c.c. of water ; reserve a little of the potassium 

 iodide solution and add the mercuric chloride solution to the 

 rest, till a permanent precipitate is formed ; then add the 

 remainder of the potassium iodide solution and cautiously drop 

 in mercuric chloride solution, till a faint permanent precipitate is 

 left. Dissolve 160 grammes of potassium hydroxide in water, 

 cool it, and add this solution to the mercury potassium iodide 

 solution and make up to 1 litre. The solution is more sensitive 

 the lower the temperature at which it is prepared, and also if 

 a little more mercuric chloride solution is added. The solution is 

 left to settle and the clear portion decanted for use. 



Standard Ammouiuin 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. = O'OOOOl gramme NH.,. 



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 O'Ol 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 usefid 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 

 '•aUcylate, 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 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 dUute to 50 c.c. 

 Compare the colours produced in Nessler cylinders and calculate 

 in the same manner as directed under Free and albuminoid 

 ammonia. 



Standard Potassium Nitrate Solution. — Dissolve 185 

 grammes of pure potassium nitrate in 1 litre of water ; dilute 

 30 c.c. to 1 litre for use. 1 c.c. = 0-00003 gramme NoOj. 



