318 Royal Society : — 



may be freely handled and exposed to the air with scarcely any 

 further change. An oxidized surface applied to the tongue is very 

 biting and caustic, and has a sweetish metallic taste. It is the 

 softest known metal admitting of free exposure to the atmosphere, 

 being scratched by soft lead with the greatest ease. It makes a 

 dark blue mark upon paper, rapidly turning yellow, which in the 

 course of a few hours nearly fades out, but can be restored with 

 sulphide of ammonium. It has little tenacity, is very malleable, 

 and may be readily pressed into wire. 



The specific gravity of thallium varies from 11 '81 to 11*91, and 

 it is probably capable of still greater condensation. 



When freshly prepared, thallium wire is perfectly amorphous, 

 but when kept in water it gradually assumes a superficial crystalline 

 appearance : this effect is immediately produced when thallium in 

 wire, ingot, or plate, tarnished or clean, is boiled in water. 



Its melting-point is 550° F., being between bismuth and lead, 

 and the metal does not become pasty before undergoing complete 

 fusion. Two pieces of clean metal weld together by pressure in the 

 cold. It begins to volatilize at a red heat, and boils below a white 

 heat ; it may be distilled in a current of hydrogen. 



It is a pretty good conductor of heat and electricity, and stands 

 electro-chemically very near cadmium. It is strongly diamagnetic, 

 ranking in this respect near bismuth. The alloys which thallium 

 forms with different metals are next described. 



Further details are given respecting the spectrum of thallium : 

 the characteristic green line is perfectly single under a very high 

 magnifying power and after refraction through nine heavy glass 

 prisms] and no new lines make their appearance at the temperature 

 of the oxyhydrogen blowpipe, — although, with the electric spark, 

 Dr. Miller has shown that several new lines come into existence. 



The delicacy of the optical test for thallium is roughly estimated, 

 the * th of a grain being easily perceptible. 



5,000,000 ° ... . 



The atomic weight of thallium is given as 203, being the mean of 

 five experiments. The author states, however, that this is not to 

 be regarded as a final result. 



The chemical properties of thallium are next described. It does 

 not decompose water even at the boiling-point, but remains bright 

 under this liquid. The superficial tarnish is a powerful base so- 

 luble in water, and reacting like an alkaline solution. Melted in 

 the air, thallium forms a readily fusible oxide, its behaviour re- 

 sembling that of lead. 



The formation of thallic acid and the properties of some of the 

 thallates are described. Sulphate, nitrate, the chlorides, sulphide, 

 iodide, and other salts of thallium are described in detail. The 

 metal may be quantitatively determined by precipitation, either as 

 protochloride, iodide, or platinochloride. 



The position of thallium amongst elementary bodies is then dis- 

 cussed. Although one or two of its properties show a resemblance 

 to the alkaline metals, the author does not agree with continental 

 chemists in classing it with this group, — numerous facts proving 



