458 PRINCIPLES OF CHEMISTRY 



by passing chlorine through a series of Woulfe's Lotties, or into an 

 inverted retort filled with water. Under the action of light, chlorine 

 water gives oxygen and hydrochloric acid. At a saturated solution 

 of chlorine yields a crystallo-hydrate, CL ; ,8H. 2 O, which easily splits up 

 into chlorine and water when heated, so that if it be fused up in a tube 

 and heated to 35 two layers of liquids are formed a lower stratum 

 of chlorine containing a small quantity of water, and an upper stratum 

 of water containing a small quantity of chlorine. 10 



Chlorine explodes with hydroyen, if a mixture of equal volumes be 

 exposed to the direct action of the sun's rays 1 1 or brought into contact 

 with spongy platinum, or a strongly-heated substance, or subjected to 

 the action of an electric spark. The explosion in this case takes place 



10 According to Faraday's data the hydrate of chlorine contains CL,10H.,O, but Rooze- 

 boom (1885) showed that it is poorer in water CL,8!L,O. At. first small, almost 

 colourless, crystals are obtained, but they gradually form (if the temperature be below 

 their critical point 28'7, above which they do not exist) large yellow crystals, like those of 

 potassium chromate. The specific gravity is T23. The hydrate is formed if there be 

 more chlorine in a solution than it is able to dissolve under the dissociation pressure 

 corresponding with a given temperature. In the presence of the hydrate the percentage 

 amount of chlorine at = 0'5, 9 3 = 0'9, and at 20 = 1'82. At temperatures below 9 the 

 solubility (determined by Gay-Lussac and Pelouze, see Note 9) is dependent on the forma- 

 tion of the hydrate; whilst at higher temperatures under the ordinary pressure the 

 hydrate cannot be formed, and the solubility of chlorine falls, as it does for all gases 

 (Chapter L). If the crystallo-hydrate is not formed, then below 9 the solubility follows 

 the same rule (6 1'07 p.c. Cl, 9 0'95 p.c.). According to Roozeboom the chlorine evolved 

 by the hydrate presents the following tensions of dissociation at = 249 mm., at 4 = 398, 

 at 8 = 620, at 10 = 797, at 14 = 1400 mm. In this case a portion of the crystallo-hydvate 

 remains solid. At 9' 6 the tension of dissociation is equal to the atmospheric pressure. At 

 a higher pressure the crystallo-hydrate may form at temperatures above 9 up to 28'7, 

 when the vapour tension of the hydrate equals the tension of the chlorine. It is evident 

 that the equilibrium which is established is on the one hand a case of a complex hetero- 

 geneous system, and on the other hand a case of the solution of solid and gase<m> 

 substances in water. 



The crystallo-hydrate or chlorine water must be kept in the dark, or the access of light 

 be prevented by coloured glass, otherwise oxygen is evolved and hydrochloric acid 

 formed. 



11 The chemical action of light on a mixture of chlorine and hydrogen was discovered 

 by Gay-Lussac and Draper (1809). It has been investigated by many, and especially l>y 

 Draper, Bunsen, and Roscoe. Electric or magnesium light, or the light emitted by the 

 combustion of carbon bisulphide in nitric oxide, and in general that which forms photo- 

 graphic images, acts in the same manner as sunlight, according to the intensity. At 

 temperatures below 12 light no longer brings about reaction, or at all events does not 

 give an explosion. It was long supposed that chlorine that had been subjected to tin- 

 action of light was afterwards able to act on hydrogen in the dark, but it was shown that 

 this only takes place with moist chlorine, and depends on the formation of oxides of chlo- 

 rine. The presence of foreign gases, and even of excess of chlorine or of hydrogen, very 

 much enfeebles the explosion, and therefore the experiment is conducted with a detonat- 

 ing mixture prepared by the action of an electric current on a strong solution isp. gr. 1'15) 

 of hydrochloric acid, in which case the water is not decomposed that is, no oxygen is 

 mixed with the chlorine. 



