M. Lamy on Thallium. 379 



According to Lamy*, phosphoric acid forms with thallium a 

 series of phosphates, for the most part very soluble, and varied 

 in their composition and properties like the corresponding com- 

 pounds of the alkaline metals. They are as follows : — 



Neutral phosphate of thallium . PO 5 , 2T10„ HO + HO 



Acid „ '„ . PO 5 , TIO, 2 HO 



Basic „ „ . P0 5 ,3T10 



Neutral pyrophosphate „ . PO 5 , 2T10 



Acid pyrophosphate „ . PO 5 , TIO, HO 



Metaphosphate „ . PO 5 , TIO. 



All these salts are white, and almost all soluble in water and 

 insoluble in alcohol. They are distinguished from the alkaline 

 phosphates by the fact that they give a white precipitate with 

 hydrochloric acid, and also with nitric acid, provided their solu- 

 tions are neither too hot nor too dilute. The phosphates and 

 pyrophosphates give a white precipitate of tribasic phosphate 

 with the alkalies, while they are not precipitated by alkaline car- 

 bonates, nor even by alkalies in the presence of these carbonates. 



After a description of these phosphates, M. Lamy offers some 

 considerations on the position of thallium. In previous re- 

 searches on thallium he had classed this metal by the side of the 

 alkaline metals, in which he had the countenance of M. Dumas. 

 Mr. Crookes, on the other hand, places thallium near the heavy 

 metals — principally on account of the insolubility of some com- 

 pounds, such as the peroxide, the protochloride, the iodide, sul- 

 phate, and phosphate of thallium, the facility with which the pro- 

 toxide is dehydrated and loses most of its solubility, the high 

 atomic weight of the metal, the ready reduction of its salts by 

 zinc, and generally most of its physical properties. 



M. Lamy, while admitting the insolubility of its bromide, &c., 

 points out that thallium forms soluble higher chlorides, a soluble 

 fluoride, and a soluble double fluoride with silicium. He thinks 

 the physical properties of secondary importance, but principally 

 relies in support of his view on the following considerations. 



The hydrated protoxide of thallium is very soluble in water, 

 strongly alkaline and caustic like potash ; its carbonate is soluble 

 and alkaline like that of potash ; there are phosphates and arse- 

 niates various in composition and properties, like the correspond- 

 ing alkaline compounds ; the sulphate is soluble, and has most 

 of the properties of sulphate of potash, with which it is isomor- 

 phous ; there is analogy of properties and isomorphism in the 

 case of the thallium and potassium alums; and this analogy is 

 also met with in the case of the double sulphates of the magnesia 



* Comptes Rendus, April 10, 1865. 

 2C2 



