1863.] 439 



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 diamaguetic, 

 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 oxy hydrogen 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 5>0 - 0,00 o th of a 8 rain bein 8 easilv perceptible. 



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 

 that its true position is by the side of mercury, lead, or silver. The 

 ready dehydration of its basic oxide; the insolubility of its sulphide, 

 iodide, chloride, bromide, chromate, phosphate, sulphocyanide, and 

 ferrocyanide ; its great atomic weight ; its ready reduction by zinc 



