48 TECHNICAL DBUG STUDIES. 



formed by spontaneous oxidation; of the many indicators tried 

 phenolphthalein alone gave satisfactory results. 



It can readily be seen that inasmuch as the formaldehyde eliminates 

 the ammonium ion as a factor so far as the titration is concerned, the 

 result obtained will always express the total acid present, either free 

 or combined with ammonia. In the absence of organic acids an 

 additional titration without formaldehyde, using methyl orange as 

 indicator, will show whether, and to what extent, either the acid or 

 the ammonia is in excess. 



It is hardly necessary to point out that this method is applicable 

 not only to relatively pure ammonium salts, but also to many mixtures 

 containing such, provided they do not contain salts of metals precip- 

 itable by alkaline hydroxids. The method was tested on the follow- 

 ing ammonium salts with satisfactory results: Ammonium chlorid, 

 bromid, iodid, fluorid, sulphate, acetate, oxalate, citrate, thiocyanate, 

 and molybdate. 



The method was also tested by using known quantities of standard- 

 ized acids, hydrochloric, sulphuric, nitric, and oxalic, neutralizing 

 these either partly or completely, with an excess of ammonium hy- 

 droxid and then titrating as previously described in the presence of 

 sufficient formaldehyde and a few drops of phenolphthalein with 

 standard sodium hydroxid. 



In the well-founded opinion of Schiff, formaldehyde in reacting 

 upon ammonium salts forms hexamethylentetramin according to the 

 following equation : 



4NH 4 C1 + 6CH 2 O = 4HC1 + N (CH 2 N + CH a ), + 6 H 2 O 



During the reaction, especially in the case of weaker acids, much 

 heat is evolved, and the avidity of the formaldehyde for the ammonium 

 ion is so great that an aqueous solution of ammonium acetate, for 

 instance (which ordinarily on heating gives off considerable ammonia) 

 on boiling with formaldehyde in excess loses nearly all of its acetic 

 acid, hexamethylentetramin remaining. 



