186 QUANTITATIVE ANALYSIS. 



Preparation of the Tenth-normal Ammonia Solution. 



Dilute 8 cc. of a concentrated solution of ammonia, specific 

 gravity 0.9, to 1100 cc. Determine the strength of this dilute 

 solution by titrating against 10 cc. portions of the standard 

 N/5 hydrochloric acid, using a dilute solution of cochineal * 

 as the indicator. 



Example: 10 cc. of the standard N/5 HC1 required 18.8 cc. 

 of the NH 3 solution to exactly neutralize it (mean of two 

 duplicate determinations). 



NH 3 +HC1=NH 4 C1. 10 cc. N/5 HC1 contain 0.07292 g. HC1. 



17.07 36.46 



/. 36.46 : 17.07 : : 0.07292 :z; 

 x = 0.03414 g. NH 3 in 18.8 cc. 



x 



7777, = 0.001816 g. NH 3 in each cubic centimeter, or 

 io.o 



1.816 g. of NH 3 per liter. 



This may be made exactly a tenth-normal solution contain- 

 ing 1.707 g. of NH 3 per liter, as follows: 



1.707 : 1000 : : 1.816 : x; x = 1063.9 cc. 

 /. z-1000cc. = 63.9cc. 



Hence by adding 63.9 cc. of distilled water to exactly one 

 liter of the dilute ammonia solution (found to contain 1.816 

 g. NH 3 per liter) the 1063.9 cc. of ammonia solution result- 

 ing will be exactly tenth-normal. 



Ten cubic centimeters of the fifth-normal hydrochloric acid 

 solution should be exactly neutralized by 20 cc. of the tenth- 

 normal ammonia solution, using cochineal as the indicator. 



1 This solution of cochineal is prepared by digesting 3 grams of pow- 

 dered cochineal in a mixture of 50 cc. of strong alcohol and 200 cc. of 

 distilled water for a day or two at ordinary temperature. During the 

 digestion the mixture should be frequently shaken. The filtered solution 

 is employed as the indicator. 



