92 METHODS OF DETERMINING ALKALI 



If less than 40 mg. of nitric nitrogen is to be determined, 

 it is well to take a. correspondingly smaller quantity of 

 iron and sulphuric acid. The neck of the reduction flask 

 is fitted with a 2-hole stopper through which passes a 

 50-cc. separatory funnel and a bent tube which dips into 

 a vessel containing water to prevent mechanical loss. 

 The acid is slowly added and allowed to stand until the 

 rapid evolution of hydrogen is over and then heated to 

 boiling for ten minutes. The contents of the side vessel 

 should be returned to the reduction flask before the re- 

 action is complete, thus insuring the complete reduction 

 of any nitrates which may have been carried over with 

 the first violent evolution of the hydrogen. The contents 

 of the reduction flask are transferred to a Kjeldahl flask, 

 neutralized with sodium hydroxide, and distilled into 

 standard acid. The excess of acid is titrated back with 

 standard alkali, lacmoid being used as indicator." 



Nitrates should be determined immediately after sam- 

 pling unless some sterilizing material, such as chloroform, 

 is added to check bacterial activity. 



Determination of Bases. - Calcium. - - The common 

 method for determining calcium is to heat a given 

 quantity of the solution nearly to boiling, and, after 

 adding a few drops of ammonia, to precipitate the 

 calcium completely by adding, drop by drop, a hot 

 solution of ammonium oxalate. The solution is kept 

 at this temperature for about 2 hours after which tw r o 

 or three decantations with hot water from the beaker 

 containing the solution are passed through a filter. The 

 precipitate remaining in the beaker is dissolved with a few 

 drops of hydrochloric acid, water is added, and the former 

 process of adding ammonia and ammonium oxalate to 

 reprecipitate the calcium is repeated. The solution, to- 



