464 PRINCIPLES OF CHEMISTRY 



a solution of chlorine is termed * chlorine water ; * and is employed in 

 ak diluted form in medicine and as a laboratory reagent. It is pre- 

 pared by passing chlorine through a series of Woulfe's bottles or into 

 an inverted retort filled with water, tinder the action of light, chlorine 

 water gives oxygen and hydrochloric acid. At a saturated solution 

 of chlorine yields a crystallo-hydrate, C1 2 ,8H 2 O, which easily splits up 

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

 and heated to 35, two layers of liquid 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 hydrogen, if a mixture of equal volumes be 

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



an increase of solubility with tlie progress of time. Schonbein and others suppose that 

 chlorine acts on water, forming hypochlorous and hypochloric acids, (HC10 + HC1) 



The equilibrium between chlorine and steam as gases and between water, liquid 

 chlorine, ice, and the solid crystallo-hydrate of chlorine is evidently very complex. Gibbs, 

 Guldberg (1870) and others gave a theory for similar states of equilibrium, which was after- 

 wards developed by Roozeboom (1887), but it would be inopportune here to enter into its 

 details. It will be sufficient in the first place to mention that there is now no doubt 

 (according to the theory of heat, and the direct observations of Ramsay and Young) that 

 the vapour tensions at one and the same temperature are different for the liquid and 

 solid states of substances ; secondly, to call attention to the following note ; and, thirdly, 

 to state that, in the presence of the crystallo-hydrate, water between 3> 24 and + 28'7 

 (when the hydrate and a solution may occur simultaneously) dissolves a different amount 

 of chlorine than it does in the absence of the crystallo-hydrate. 



10 According to Faraday's data the hydrate of chlorine contains C1 2 ,10H 2 O, but Rooze- 

 boom (1885) showed that it is poorer in water and = C1 2 ,8H 2 O, At first small, almost 

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

 fcheir critical point 28 0< 7, above which they do not exist) large yellow crystals, like those of 

 potassium chromate. The specific gravity is 1-23. 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, at 9 = 0'9, and at 20 = T82. 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 I.). 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 = 1,400 mm. In this case a portion of the crystallo-hydrate 

 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 gaseous 

 aubstances 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 ev'olved and hydrochloric acid 

 formed. 



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

 Gay-Lussac and Tlu-nard (1809). It has'bee-n investigated by many savants, and especially 



