A METHOD FOR TESTING AMMONIUM SALTS. 

 By B. HERSTEIN. 



While titrating acid solutions containing both formaldehyde and 

 ammonium salts serious discrepancies in the results were noticed, and 

 in 1909 an extended investigation of the phenomena was begun. It 

 was soon found that formaldehyde acts upon ammonium salts in the 

 same way as it does upon ammonium hydroxid, namely, by forming 

 hexamethylentetramin. It was also found that in the presence of a suf- 

 ficient quantity of formaldehyde the ammonium ion is liberated from 

 the acid with which it has been combined, and the latter thus becomes 

 titratable with a standard solution of sodium or potassium hydroxid, 

 using phenolphthalein as indicator. 



In a paper entitled, "Trennung von Amin- und Sauref unction in 

 Losungen von Aminsauren mittelst Formaldehyd," Schiff reported 

 the same reaction and later based thereon a method for determining 

 formaldehyde. 6 He also stated that this reaction may be utilized in- 

 versely,that is, for determining ammonium salts by means of formalde- 

 hyde, but no details are given. A. Ronchese c studied this reaction more 

 carefully and recommends it as a method for determining ammonia. 

 He uses, however, an unnecessarily large excess of formaldehyde 

 which tends seriously to impair the results. In view of the fact that 

 ammonium salts play a very important part in every chemical labora- 

 tory, an easy method for their quantitative determination is very 

 desirable. The best method hitherto available was to add an excess 

 of standard fixed alkali, heat until all the ammonia is expelled, and then 

 titrate back the excess of alkali used by means of a standardized acid 

 solution. This method has disadvantages, chief among which is the 

 time required to drive off all ammonia. The following method 

 requires a minimum amount of time and yet gives satisfactory results : 



A weighed quantity, about 1 gram, of any ammonium salt is dis- 

 solved in approximately 50 cc of water, 3 or 4 cc of a perfectly neutral 

 40 per cent solution of formaldehyde, and a few drops of phenolphtha- 

 lein are added, and titrated with a standard solution of a fixed alkali 

 until the pink color remains permanent after the solution has been 

 brought to boiling. The previous neutralization of formaldehyde is 

 necessary, because it almost invariably contains some formic acid 



a Liebig's Annalen der chemie, 1901 ; 819 : 76. <= J. chim. pharm., 1907 (6) 25 : 611. 



6 Cbera, Ztg., 1903, 27 (l) : 13 



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