366 Gooch and Mo Clenahan— Typical Hydrous Chlorides. 



the hydrous chloride in an atmosphere of hydrogen chloride, 

 but at the temperature of incipient redness at which Dumas 

 worked the reversal of the hydrolytic effect is slow and difficult. 



In the case of a hydrous chloride, like barium chloride, 

 which shows no tendency to undergo hydrolytic decomposition 

 at temperatures at which the water is completely removed, there 

 seems to be no reason for anticipating any marked effect upon 

 the progress of the dehydration when hydrogen chloride is made 

 the surrounding atmosphere instead of air. With a hydrous 

 chloride which evolves hydrogen chloride at the temperature 

 of dehydration and forms an oxychloride, oxide or hydroxide 

 the case is different. In such a case the effect of enormously 

 increasing the concentration of hydrogen chloride in the system 

 at the temperatures of incipient hydrolysis will naturally be to 

 restrain the hydrolysis ; but whether the result will be the 

 formation of a chloride of lower content of water or an 

 increased stability of the hydrous chloride for some range of 

 temperature will turn upon the affinity of the anhydrous chlor- 

 ide for water. 



In the process of dehydrating hydrous aluminum chloride, 

 for example, an increase in the concentration of hydrogen chlor- 

 ide in the system will tend to retard the exchange of hydroxy 1 

 for chlorine at the temperature of incipient hydrolysis; but 

 whether the result of such retardation will be the formation of 

 the anhydrous chloride or simply an extension of the range 

 of temperature for which the original hydrous chloride is stable 

 is not immediately obvious, though the high degree of attrac- 

 tion existing between anhydrous aluminum chloride and water, 

 as indicated in the large heat of hydration of that salt, would 

 seem to suggest the latter alternative. 



In the work of which an account follows the effect of sub- 

 stituting an atmosphere of hydrogen chloride for ordinary air in 

 experiments upon the dehydration of typical hydrous chlorides 

 was studied. Barium chloride as the representative of salts 

 which lose water without other decomposition, magnesium 

 chloride which suffers some loss of chlorine when fully dehy- 

 drated, and aluminum chloride which loses all its chlorine 

 when similarly dehydrated, were the hydrous chlorides taken 

 for these experiments. 



In these experiments two combustion tubes of large size set 

 horizontally side by side in a tubulated paraffine bath served 

 as heating chambers. Each tube was fitted with a thermometer 

 and connected through a drying bulb and column with an aspi- 

 rator. Portions of the hydrous chloride to be treated were 

 weighed into porcelain boats. One of these boats was inserted 

 in each tube about midway in the bath (heated to a regulated 

 temperature) and immediately below the bulb of the thermom- 



