110 McClenahan — Hydrous Thallic Chloride. 



chloride is small, while the addition of hydrogen chloride is rela- 

 tively considerable. For this range of temperature in an atmos- 

 phere of hydrogen chloride, the constitution of the salt corre- 

 sponds to the symbol of the chlorthallic acid, TlCl 3 '3H 2 OHCl, 

 with some of the liberated water retained by the hygroscopic 

 compound. At 60° and 70° this hygroscopic water volatilizes and 

 the substance has, approximately, the composition represented 

 by the symbol TlCl 3 '3H 2 OHCl ; at 80° the composition sug- 

 gests the formation of some TlCl 3 -H 2 OHCl ; while at 90° 

 hydrogen chloride with more water is leaving the salt, and at 

 100° after an hour's heating, and at 110° after a half hour, the 

 composition corresponds to a mixture of salts, TlCl 3 'H 2 OHCl 

 and perhaps some TlCl 3 '3H 2 OHCl with T1C1 3 'H 2 0. At 115° 

 after a half hour the hydrogen chloride is nearly gone and the 

 further dehydration of T1C1 3 'H 2 has begun ; and at 120° the 

 product is practically the anhydrous salt, T1C1 3 , slightly reduced 

 to the thallous-thallic chloride. When a comparison is insti- 

 tuted between the results obtained by heating the salt in air to 

 temperatures above 100°, where the chlorthallic acid is break- 

 ing down, and those obtained under similar conditions of tem- 

 perature in hydrogen chloride, it is obvious that dehydration 

 of the salt T1C1 3 'H 2 is inhibited by an environment of hydro- 

 gen chloride. 



Reverting now to Cushman's diagram* of the results 

 obtained by long exposure of the hydrated thallic chloride, 

 T1C1 3 '4H 2 0, in desiccators at the ordinary temperature, it 

 appears that two molecules of water disappeared from 

 the salt in the course of a week, that the third molecule 

 required for its removal five weeks, and that the fourth mole- 

 cule vanished only after fifteen weeks more. The general 

 order of the phenomena is in accord with the observations 

 recorded above for the behavior of the salt at higher tempera- 

 tures during the interval of an hour. 



As appears from Cushman's diagram, the preparation of the 

 dehydrated chloride, T1C1 3 *2H 2 0, should be very easy. This 

 salt was therefore made the starting point of a series of experi- 

 ments upon the rate of dehydration in air. A new sample of 

 the chloride, T1C1 3 '4H 2 0, was crystallized out and this was desic- 

 cated over calcium chloride for three days, until upon analysis 

 the residue was found to have the constitution shown by the 

 symbol T1C1 3 *2H 2 0. In this analysis the chlorine was deter- 

 mined, as usual, in the form of silver chloride, precipitated in 

 presence of a sufficiency of nitric acid, and the thallium was 

 estimated as the light yellow thallium chlorplatinate precipi- 

 tated by chlorplatinic acid from the solution of the thallous 

 salt reduced by sulphur dioxide and weighed on asbestos. 



* Loc. cit. 



