376 Mr Fent&n, On a new method [Mar. 15, 



Carbamates differ in this respect from all other substances yet 

 studied, and the actions serve to detect and estimate them in 

 presence of ammonia, urea, &c. 



It appeared probable therefore, that if a soluble bromide were 

 added to a mixture of sodium carbamate and hypochlorite, nitrogen 

 should be evolved, by reason of the hypobromite formed in solu- 

 tion* potentially or actually. This is found to be the case. 



A solution of sodium carbamate may be prepared 



1st. By dissolving ammonium carbamate in a strong solution 

 of sodium hydroxide, and allowing the mixture to stand for one or 

 two days over strong sulphuric acid under a bell-jar. 



CONH 2 ONH 4 + NaOH = CONH 2 ONa + OH 2 + NH 3 . 



2nd. By dissolving ammonium carbamate in solution of sodium 

 hydroxide and adding a slight excess of sodium hypochlorite. 

 2CONH 2 ON H 4 + 3NaC10 + 2NaOH 

 = 2CONH 2 ONa + 3NaCl + 50H 2 + N 2 . 



3rd. By Drechsel's method, namely by adding an alcoholic 

 solution of sodium ethylate to ammonium carbamate dissolved in 

 aqueous ammonia. 



If to a solution of sodium carbamate, prepared by any of these 

 methods, an excess of sodium hypochlorite (and, if necessary, 

 sodium hydroxide) be added, and the liquid shaken until bubbles 

 of gas (due to traces of ammonia) cease to be evolved, the mixture 

 may be kept for hours with hardly appreciable decomposition ; but 

 the addition of a soluble bromide will cause a copious evolution of 

 nitrogen — immediately if the quantity of bromide is considerable, 

 and more slowly with small quantities. 



This reaction, then, serves to detect bromides in presence of 

 unlimited quantities of chlorides, hypochlorites &c. Iodides appear 

 to give a slight action, but so slowly in comparison with bromides 

 that it seems not improbably due to contamination with bromide. 

 I have not succeeded, however, in obtaining a specimen of iodide 

 which gives no action at all. 



Where traces of bromide have to be looked for, it is advisable 

 to make a blank comparative test, since there is usually a very 

 slight decomposition of the carbamate solution, which might be 

 misleading. Equal volumes of a solution of sodium carbamate, 

 sodium hypochlorite in excess, and sodium hydroxide, are placed 

 in two long tubes. The suspected liquid added to one, and an 

 equal volume of distilled water to the other. The tubes are 

 shaken and allowed to stand for some time (10 minutes to 1 

 hour according to quantity). On again shaking, a few bubbles 

 only will appear in the tube containing the blank test, whilst if 

 bromide is present there will be a considerable effervescence in 

 the other tube, due to evolution of nitrogen. 



* Lyons, Pharmaceutical Record, May, 1885. 



