42 PUBLIC HEALTH CHEMISTRY 



Take three 50 c.c. Nessler glasses, and from a burette add 

 to the first I c.c., to the second 2 c.c., and to the third 

 3 c.c. of standard solution of ammonium chloride ; I c.c. 

 = o-oi mgr. NH 3 . Fill all three up to the 50 c.c. mark 

 with ammonia-free distilled water, and then add to each 

 2 c.c. of Nessler solution, and mix. Put these glasses, 

 distinctively marked, on the slab or shelf, and compare 

 the first 50 c.c. of distillate with them as to depth of 

 coloration. If the distillate matches any one of them, 

 the result is attained. If it does not match any of them, 

 it may be intermediate between any two of them, or be 

 darker than the 3 c.c. or lighter than the i c.c. glass. In 

 any case, fresh trial glasses should be put up for, as the 

 case may be, -5 c.c., 1-5 c.c., 2-5 c.c., 4 c.c., 5 c.c., 6 c.c., 

 of standard solution. If the distillate is darker than the 

 coloration given by 6 c.c. of standard solution, it is better 

 to dilute it with ammonia-free distilled water, and then to 

 proceed to match. The same procedure is carried out 

 with the second 50 c.c. of distillate and succeeding lots. 

 The distillation is stopped when no coloration is given 

 with 2 c.c. of Nessler, or at least less than will match 0-5 c.c. 

 of standard solution. This usually happens with the 

 fourth lot of 50 c.c. The sum of the amounts of ammonia 

 found in each lot of distillate, is the total free and saline 

 ammonia present in 500 c.c. of sample water. This is 

 reduced to the amount in 100 c.c., and thereafter expressed 

 as parts of ammonia per 100,000. The distilling over in 

 separate lots is the mode recommended by the Society of 

 Public Analysts, but Wanklyn recommends that only 

 50 c.c. be distilled, and that the amount found in it be 

 increased by one-third, on the ground that in his experience 

 three-fourths of the ammonia comes over in the first lot 

 of 50 c.c. 



EXAMPLE. 



First 50 c.c. of dist. matched 5.0 c.c. std. sol. of NH 4 C1. 

 Second 50 c.c. do. do. 1-5 c.c. do. do. 



Third 50 c.c. do. do. 0-5 c.c. do. do. 



Fourth 50 c.c. do. do. nil 



7-0 c.c. do. do. 



