THE HALOGENS 471 



coming into contact with the turpentine, give feeble explosions, which 

 are in no way dangerous, owing to the small mass of the substance 

 formed. The drops of chloride of nitrogen may, with great precaution, 

 be collected for investigation in the following manner. The neck of a 

 f mmel is immersed in a basin containing mercury, and, first, a saturated 

 solution of common salt is poured into the funnel, and above it a solu- 

 tion 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. It 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 phos- 

 phorus, turpentine, india-rubber, etc., causes an explosion, which is 

 .sometimes so violent that a small drop will pierce through a thick 

 board. The exceeding facility of the decomposability of chloride of 

 nitrogen is connected with the fact that it is formed with an absorption 

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

 38000 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 formed, so that the reaction 

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

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

 taneously formed : 2NaHO + Cl 2 =NaCl + NaCIO + H 2 O. The resultant 

 solution 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 + 2Cl 2 =CaCl 2 O 2 + CaCl 2 + 2H 2 O. A mixture 

 of the product of metalepsis and calcium chloride is obtained. This 

 mixture is employed in practice on a large scale, and is termed ' bleach- 

 ing powder,' owing to its acting, especially when mixed with acids, as a 

 bleaching agent on tissues, so that it resembles chlorine in this respect, 

 but is preferable to chlorine, because the destructive action of the 

 -chlorine may 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 this substance 

 is obtained from chlorine and hydrate of lime, and contains 30 both 



50 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 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 obtained contains not less than three equivalents 

 of calcium hydroxide to four equivalents of chlorine, so that its composition is 

 {Ca(HO) 2 ]3Cl 4 . In all probability a simple absorption of chlorine by the lime at first 

 tiakes place in this case, as may be seen from the fact that even carbonic anhydride, when 



