THE HALOGENS 477 



Chloride of nitrogen is a yellow oily liquid of sp. gr. 1*65, which 

 boils at 71, and breaks up into N + C1 3 at 97. The contact of 

 phosphorus, turpentine, india-rubber, &c. causes an explosion, which 

 is sometimes, so violent that a small drop will pierce through a thick 

 board. The great ease with which chloride of nitrogen decomposes is 

 dependent upon the fact that it is formed with an absorption of heat, 

 which it evolves when decomposed, to the amount of about 38.000 heat 

 units for NC1 3 , as Deville and Hautefeuille determined. 



Chlorine, when absorbed by a solution of caustic soda (and also of 

 other alkalis) at the ordinary temperature, causes the replacement of 

 the hydrogen in the caustic soda by the chlorine, with the formation 

 of sodium chloride by the hydrochloric acid, so that the reaction 

 may be represented in two phases, as described above. In this 

 manner, sodium hypochlorite, NaCIO, and sodium chloride are simul- 

 taneously formed : 2NaHO + C1 2 = NaCl -f NaCIO + H 2 O. The 

 resultant solution contains NaCIO and is termed ' eau de Javelle. An 

 exactly similar reaction takes place when chlorine is passed over dry 

 hydrate of lime at the ordinary temperature : 2Ca(HO) 2 -f 2C1 2 

 = CaCl 2 O 2 + CaCl 2 + 2H 2 O. A mixture of the product of metalepsis 

 with calcium chloride is obtained. This mixture is employed in practice 

 on a large scale, and is termed ' bleaching powder, owing to its acting, 

 especially when mixed with acids, as a bleaching agent on tissues, so 

 that it resembles chlorine in this respect. It is however preferable 

 to chlorine, because the destructive action of the chlorine can be 

 moderated in this case, and because it is much more convenient to deal 

 with a solid substance than with gaseous chlorine. Bleaching powder 

 is also called chloride of lime, because it is obtained from chlorine 

 and hydrate of lime, and contains 30 both these substances. It 



find above it a solution of sal-ammoniac in 9 parts of water. Chlorine is then slowly 

 passed through the solutions, when drops of chloride of nitrogen fall into the salt 

 water. 



80 Quicklime, CaO (or calcium carbonate, CaCO 5 ), does not absorb chlorine when cold, 

 .but at a red heat, in a current of chlorine, it forms calcium chloride, with the evolution 

 of oxygen. (This was confirmed in 1898 by Wells, at Oxford.) This reaction corresponds 

 with the decomposing action of chlorine on methane, ammonia, and water. Slaked lime 

 (calcium hydroxide, CaH 2 O 2 ) also, when dry, does not absorb chlorine at 100. The 

 absorption proceeds at the ordinary temperature (below 40). The dry mass thus ob- 

 tained contains not less than three equivalents of calcium hydroxide to four equivalents 

 of chlorine, so that its composition is [Ca(HO) 2 ] 3 Cl 4 . In all probability a simple absorp- 

 tion of chlorine by the lime at first takes place in this case, as may be seen from the fact 

 that even carbonic anhydride, when acting on the dry mass obtained as above, disengages 

 all the chlorine from it, leaving only calcium carbonate. But if the bleaching powder be 

 obtained by a wet method, or if it be dissolved in water (in which it is very soluble), and 

 carbonic anhydride be passed into it, then chlorine is no longer disengaged, but chlorine 

 oxide, CLjO, and only half of the chlorine is converted into this oxide, while the other half 

 remains in the liquid as calcium chloride. From this it may be inferred that calcium 



