470 PRINCIPLES OF CHEMISTRY 



panied by the formation of sal-ammoniac, 8 

 But if the ammonium salt be in excess, then the reaction proceeds with 

 the replacement of the hydrogen in the ammonia by chlorine. The 

 essence of the matter is that NH 3 + 3C1, forms NC1 ;J -f 3HC1. 29 The 

 resulting product of metalepsis, or chloride of nitrogen, NC1 3 , dis- 

 covered by Dulong, is a liquid having the property of decomposing 

 with excessive ease not only when heated, but even under the action 

 of mechanical influences, as by a blow or the contact of certain solid 

 substances. The explosion which accompanies the decomposition is due 

 to the fact that the liquid chloride of nitrogen gives gaseous products, 

 nitrogen and chlorine ; a large volume of gas is evolved instantaneously 

 and causes the explosion. It is even dangerous to prepare this sub- 

 stance in any considerable quantity. Whenever an ammoniacal sub- 

 stance comes into contact with chlorine great care must be taken, 

 because it might be a case of the formation of such products and a very 

 dangerous explosion. The liquid product of the metalepsis of ammonia 

 may be most safely prepared in the form of small drops by the action 

 of a galvanic current on a slightly warm solution of sal-ammoniac ; 

 chlorine is then evolved at the positive pole, and this chlorine, acting 

 on the ammonia, gradually forms the product of metalepsis, which 

 floats on the surface of the liquid (because it is borne up by the gas), 

 and if a layer of turpentine be poured on to it these small drops, on 



of nitrogen is accompanied by the emission of light and the appearance of a cloud of sal- 

 ammoniac. In all these instances there must be an excess of chlorine. 



29 The hydrochloric acid formed combines with ammonia, and therefore the result is 

 4NH 3 + 3C1 2 = NC1 3 + 3NH 4 C1. Consequently, more ammonia enters into the reaction, 

 but the metalepsical aspect of the reaction in reality only takes place with an excess of 

 ammonia in the form of the salt. If bubbles of chlorine be passed through a fine tube 

 into a vessel containing ammonia gas, then each bubble gives rise to an explosion. If, 

 however, chlorine be passed into a solution of ammonia, then the reaction first directs 

 itself towards the formation of nitrogen, because chloride of nitrogen acts on ammonia 

 like chlorine. But when sal-ammoniac begins to form, then the reaction directs itself 

 towards the formation of chloride of nitrogen. The first action of chlorine on a solution 

 of sal-ammoniac always consists in the formation of chloride of nitrogen, which reacts on 

 ammonia thus : NC1 3 + 4NH 3 = N 2 + 3NH 4 C1. Therefore, so long as the liquid is alka- 

 line from the presence of ammonia the chief product will be nitrogen. The reaction 

 NH 4 C1 + 8C1 2 = NC1 3 + 4HC1 is reversible ; with a dilute solution it proceeds in the above- 

 described direction (perhaps owing to the affinity of the hydrochloric acid for the excess 

 of water), but with a strong solution of hydrochloric acid it takes the opposite direction 

 (probably in virtue of the affinity of hydrochloric acid for ammonia). Therefore there 

 must exist a very interesting case of equilibrium between ammonia, hydrochloric acid, 

 chlorine, water, and chloride of nitrogen which has not yet been investigated. The re- 

 action NC1 3 + 4HC1 = NH 4 C1 + 3C1 2 enabled Deville and Hautefeuille to determine the 

 composition of chloride of nitrogen. When slowly decomposed by water, chloride of 

 nitrogen gives, like a chloranhydride, nitrous acid or its anhydride 2NC1 3 + 3HoO 

 = N 2 O 3 + 6HC1. From these observations it is evident that chloride of nitrogen presents 

 great chemical interest, which is strengthened by its analogy with trichloride of phos- 

 phorus. 



