Small Quantities oj Pure Nitrogen. 247 



For such purposes the evolution of nitrogen by the inter- 

 action of one of the halogens in solution with ammonia seems 

 to be quite suitable, and employing the simple apparatus 

 described below, the gas can be obtained directly in a high 

 state of purity. In practice, bromine in dilute solution is 

 generally* employed with dilute ammonia, and the reaction 

 may be represented as 



2NH 3 + 3Br — >N 2 f+6RBr 

 and 6NH, + 6HBr — >6NH 4 Br. 



8NH 3 + 3Br 2 ->N 2 f-t-6NH 4 Br. 



Thus the end-product of the reaction ammonium bromide 

 remains in solution while the nitrogen escapes. Both the con- 

 stituents employed in the reaction can be obtained in a high 

 state of purity, and the by-products of the reaction do not 

 form sources of impurity. The evolved nitrogen is of course 

 contaminated by water-vapour and a trace of ammonia. These 

 two get absorbed by the phosphorus pentoxide kept in con- 

 nexion with the apparatus. Thus the nitrogen becomes 

 directly available in a high state of puritj'. 



The apparatus itself (fig. J) now manufactured by Messrs. 

 Cuthbert Andrews, of London, consists of a small separating 

 funnel T 1? sealed on the top of a wide-bore glass tube G with an 

 internal loop provided in it as shown at L. From the top of G 

 an outlet-tube is led off with a tap T 2 in it, beyond which a bulb 

 of P 2 5 and another tap T 3 may be employed before being- 

 sealed on to the vacuum. or other apparatus where the gas is 

 required. From about the lower end of G a side tube is led 

 off vertically, which ends in a bulb. This serves as a reservoir 

 for the ammonia to be pushed into when the gas generated 

 in G displaces it. This side tube serves also as a safety-valve 

 for the escape of any excess of gas accidentally generated 

 in G. Further, the rise of liquid in the reservoir on the 

 evolution of gas in G keeps the gas under a slight pressure, 

 so that it escapes readily on opening T 2 . A tap T 4 may also 

 be provided at the bottom of G if necessary, through which 

 to draw off the used-up ammonia prior to charging it with 

 stronger ammonia. This design of apparatus has been espe- 

 cially made with a view to avoid contamination with air. 



By adopting the following procedure, the apparatus can be 

 completely filled with the liquids, and all causes of air con- 

 tamination by bubbles locked in corners and bends removed. 



* I am indebted to Mr. Ludlam for this suggestion. 



