286 BIOLOGICAL AND SANITARY MATTERS. 



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 well mixed, 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 finally deciding 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 a; = 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 = a; X , and the amount of ammonia obtained 



z — 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 



<;alculation is slightly difierent :— Let x = the weight of ammonia 



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



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 - ~ ^. 



