286 WATER ANALYSIS. 



and collected in a stoppered bottle. So soon as the flame is 

 placed under the flask, about 250 c.c. of distilled water are placed 

 in a flask and brought to the boil (or nearly so); the flask is 

 removed to the bench, 10 grammes of caustic soda added, and, 

 when dissolution of this is complete, about half a gramme of 

 potassium permanganate dropped in. This solution of alkaline 

 permanganate is boiled, while the distillation is proceeding, 

 at such a rate, that its bulk, when 125 c.c. have distilled from 

 the flask, should be just about sufficient to make up the original 

 volume. 



The alkaline permanganate solution is added to the Wiirtz 

 flask ; and a further 125 c.c. are distilled off, and collected in a 

 second stoppered bottle. 



The first bottle contains the free (or saline) ammonia, and the 

 second the albuminoid (or organic) ammonia. 



The contents of the bottles are mixed well, and 50 c.c. of each 

 are placed in a Nessler cylinder, 2 c.c. of Nessler solution added, 

 and the tint in each of them matched by placing a known volume 

 of standard ammonium chloride solution in a Nessler cylinder, 

 making up to 50 c.c. with distilled water free from ammonia, 

 adding 2 c.c. of Nessler solution. The waters must be allowed 

 to stand for five or ten minutes before the final comparison is 

 made, as the colour does not develop instantaneously. 



After a little practice, it will be found easy to make an approxi- 

 mate match of tints at the first trial. It is not necessary to do 

 this exactly. If the cylinder which contains the distillate is of 

 approximately the same depth of shade as the standard, a little 

 may be poured from the darker cylinder till the colours are 

 matched ; the positions of the cylinders should be several times 

 reversed before deciding finally that they are equal, as a shadow 

 may be cast on one cylinder more than the other and make it 

 appear darker than it really is. 



If the cylinder containing the distillate is the darker, and 

 some of the solution has been poured from it, the calculation 

 is performed as follows : Let x = the weight of ammonia equal 

 to the amount of standard ammonia solution taken, y = the 

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

 the cylinder; then the weight of ammonia in 50 c.c. of the 



distillate = x X , and the amount of ammonia obtained 



t-y\ 



from 250 c.c. of water is found by multiplying by the total volume 

 of the distillate, which should be measured, and dividing by 50. 



If the cylinder containing the distillate is the lighter, and 

 some of the solution has been poured from the standard, the 

 calculation is slightly different : Let x = the weight of ammonia 

 equal to the amount of standard ammonia solution taken, y =the 



