58 § 47. BASES AND ACIDS WITH KE AGENTS. 



loss, titrate the acid remaining free with the standard so- 

 dic sohition, and estimate the amount of ammonia in the 

 substance analyzed, as directed in b. {Fresenius.) 



d. If the standard acid in either of these processes, 

 h or c, should contain but a very small amount of am- 

 monia, instead of titrating with soda, the determination 

 may be completed more satisfactorily with the aid of the 

 Nessler solution, by preparing a solution containing an 

 accurately known quantity of ammonia, of such a strength, 

 that about equal volumes of it and of the solution con- 

 taining the unknown amount of ammonia, will give the 

 same shade of color with equal small quantities of this 

 reagent. 



The color observations in this process are best made in 

 narrow glass cylinders of such a diameter that 100 c.c. of 

 the water to be tested form a stratum about 18 cm. deep, 

 and by placing these cylinders upon a sheet of white 

 paper near a window and looking at the surface of the 

 liquid obliquely. 



The amount of ammonia present in the solution to be 

 examined should not be great enough to give a precipi- 

 tate with the reagent, but only a coloration ; the best re- 

 sults are obtained when there is not more than one milli- 

 gramme of NHg in 100 c.c. of the solution, but even if the 

 solution is ten times stronger than this, the results are 

 more accurate than those obtained by titration ; it is im- 

 portant that the temperature of the solution tested should 

 be nearly the same as that of the other solution contain- 

 ing a known quantity of ammonia, which is made the 

 standard of comparison, and that neither free potassa or 

 soda, nor calcic or magnesic carbonate should be present. 



To estimate the ammonia in a solution by this method, 

 first make a standard solution of ammonic chloride con- 

 taining 0.3147 grm. in one litre, which is equal to 0.1 

 grm. of ammonia (NH^) in the litre ; add 1 c.c. of the 



