104 McClenahan — Hydrous Thallic Chloride. 



Art. XV. — The Constitution of Hydrous Thallic Chloride; 

 by F. M. McClenahan. , 



[Contributions from the Kent Chemical Laboratory of Yale University — 



CXIX.J 



The nature of hydration and the constitution of the hydrous 

 thallic chlorides have recently been the subject of discussion 

 by Cushman* and R. J. Meyer, f The tetrahydrated thallic 

 chloride T1C1 3 ■ 4H 2 is easily prepared, and WertherJ, and 

 R. J. Meyer record the preparation of the monohydrate 

 TIClg * H 2 0, though Cushman was unable to actually isolate 

 this salt. All assert that dehydration cannot be carried beyond 

 the condition of the monohydrate without loss of chlorine. 

 More recently Thomas§ has made record of the complete dehy- 

 dration of thallic chloride without loss of chlorine by exposure 

 for seventeen weeks over sodium hydroxide in vacuo, and ven- 

 tures the opinion that there is little ground for believing that 

 the relation of one of the molecules of water to the salt is differ- 

 ent from that of the others. Meyer maintains that one of the 

 chlorine atoms is not precipitated by silver nitrate and that it 

 sustains a relationship to the complex different from the other 

 two, so that the anhydrous salt may be represented by the 

 symbol (T1C1) Cl 2 . Cushman points out, however, that Meyer's 

 use of Volhard's titrimetric method of analysis was faulty, 

 inasmuch as the thallic salt acts as an oxidizer upon the standard 

 potassium sulphocyanate employed to estimate the silver salt 

 left over after precipitation of the chlorine by a standard solu- 

 tion of silver nitrate, and that in examinations of the nitrates 

 from the usual gravimetric determination (by silver nitrate in 

 presence of a sufficiency of nitric acid), no sign of incomplete 

 precipitation of the chlorine was observed. Cushman con- 

 cludes that the evidence which supports the writing of thallic 

 chlorides as (T1C1) Cl 2 , as well as all speculation from this 

 point of view, falls to the ground. From experiments in 

 which two specimens of a crystalline non-hygroscopic prepara- 

 tion of the tetrahydrated thallic chloride T1C1 3 . 4H 2 were 

 exposed twenty-one weeks in desiccators, the one over sul- 

 phuric acid and the other over phosphoric pentoxide, the con- 

 clusion was drawn by Cushman, that it may be taken as 

 certain that the last fourth of the water comes off slowly 



* Amer. Chem. Jour., 24, 222 (1900) ; 26, 505 (1901). 

 f Zeischer. Anorg. Chem., 32, 72 (1902). 

 % Jour, prakt. Chem., 91, 385 (1864). 

 § Compt. Eend., cxxv, 1051 (1902). 



