Gooch and MeClenahan — lyrical Hydrous Chlorides. 365 



Art. XXXIII. — The Behavior of Typical Hydrous Chlorides 

 when heated in Hydrogen Chloride • by F. A. Gooch and 

 F. M. McClenahan. 



(Contributions from the Kent Chemical Laboratory of Yale University — CXXVI.) 



The halogen salts of the metals are convertible by the action 

 of water to oxy-salts, hydroxides, or oxides with varying 

 degrees of readiness. In order that water may act hydrolyti- 

 cally upon barium chloride, for example, with liberation of 

 hydrogen chloride and substitution of oxygen for chlorine, the 

 temperature of the system must approach low redness, while 

 magnesium chloride is attacked at a much lower temperature, 

 and aluminum chloride is extremely sensitive to the metatheti- 

 cal action of water. These reactions follow the indications of 

 the heat moduli of the transformations. To effect the meta- 

 thesis between barium chloride and water, with formation of 

 barium hydroxide and hydrogen chloride, a very considerable 

 accession of energy from without the system is needed ; the 

 similar reaction between magnesium chloride and water requires 

 less reinforcement from the outside; while the reaction between 

 anhydrous aluminum chloride and water takes place easily. 

 When a hydrous chloride is heated to the temperature of decom- 

 position, the products will be the anhydrous chloride and water, 

 or hydrogen chloride and an oxychloride, oxide or hydroxide, 

 according to the nature of the particular chloride under experi- 

 mentation. Hydrous barium chloride, BaCl 2 '2H 2 0, parts with 

 all its water and becomes anhydrous at 100° C; the hydrous 

 magnesium chloride, MgCl 2 '6H 2 may lose a large part of its 

 water at temperatures considerably above 100° without apprecia- 

 able loss of chlorine, but exchanges chlorine for oxygen with 

 formation of hydrogen chloride at higher temperatures ; while 

 hydrous aluminum chloride, A1C1 3 '6II 2 0, loses water only with 

 simultaneous formation of hydrogen chloride and exchange of 

 chlorine for oxygen at 100°, and at temperatures at which all 

 water is removed is converted to aluminium oxide. 



It is obvious that in those cases in which hydrolytic decom : 

 position takes place at temperatures below those at which the 

 tendency to reversal ceases, the rate of decomposition must be 

 affected by the concentrations of the active products of decom- 

 position. So it is natural to expect that an increase in the 

 concentration of hydrogen chloride in the system will serve to 

 restrain hydrolytic action and decomposition of the chlorides 

 at temperatures of incipient hydrolysis. Dumas* tried to take 

 advantage of this principle in the preparation of anhydrous 

 magnesium chloride, free from oxide, by prolonged drying of 



* Ann. Chim. (3), lv, 137. 



Am. Jour. Sol— Fourth Series, Vol. XVII, No. 101.— Mat, 1904. 

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