METHODS. 83 



(6) Distillation. 



After cooling transfer tq distilling flasks with 

 200 cc. water and add 0.5 gm. zinc dust, 25 cc. 

 KjS solution and 50' cc. of NaOH. Connect 

 the flask with the condenser and distil until all 

 the ammonia has passed over, collecting it in 

 the standard HCl and titrating against the 

 standard alkali, using cochineal as an . indi- 

 cator. 



II. Phenolsulfonic Acid Method for Nitrates. 



1. Eeagents. 



{a) Phenolsulfonic acid. 



15 gms. phenol dissolved in a mixture of 92.5 

 cc. H2SO4 and 7.5 cc. water. 



(6) Standard Nitrate solution. 



0.7221 gms. KNOa per liter of water. 25 cc. 

 are evaporated to dryness and treated as de- 

 scribed below; the solution made up to 100 

 cc. with water, then each cc. = .025 mg. nitro- 

 gen. 



2. Determination. 



The solution in which the nitrate is to be de- 

 termined is evaporated to dryness on a water 

 bath. 2 cc. of the phenolsulfonic acid is added 

 and stirred thoroughly. 

 Stand 10-15 minutes. 



Add 15 cc. of water and 10-15 cc. of ammonium 

 hydroxid. Dilute to 100 cc. in a colorimeter 

 tube and compare with the standard solution 

 in another tube, diluting the unknown or the 

 standard as necessary. 



