186 M. Lamy on the new Metal Thallium, 



Thallium is very soft and very malleable ; it may be scratched 

 by the nail, and easily cut with a knife. It marks paper ; and 

 the mark has a yellow reflexion. Its density, 11*9, is a little 

 higher than that of lead. It melts at 290°, arid volatilizes at a 

 red heat. Lastly, thallium has a great tendency to crystallize, 

 for bars obtained by fusion emit a noise like the crackling of tin 

 when they are bent. But the physical property par excellence 

 of thallium, that which, according to Bunsen and Kirchhoff's 

 beautiful labours, characterizes the metallic element, that which 

 has led to its discovery, is the faculty it possesses of giving to 

 the colourless gas-flame a green coloration of great richness, 

 and in the spectrum of this flame a single green ray, as isolated 

 and as distinctly marked as the yellow ray of sodium or the red 

 ray of lithium. On the micrometric scale of my spectroscope 

 this ray occupies the division 120*5, that of sodium being at the 

 division 100. The least particle of thallium, or of one of its 

 salts, displays the green line with such lustre that it appears 

 white. From my determinations the g^th of a gramme can 

 be perceived in a compound. 



Thallium tarnishes rapidly in the air, becoming covered with 

 a thin pellicle of oxide, which protects the rest of the metal 

 from alteration. This oxide is soluble, distinctly alkaline, and 

 has an odour and taste like those of the alkaline metals. 



Thallium is attacked by chlorine, slowly at the ordinary tem- 

 perature, but rapidly at a temperature above 200°. The metal 

 then melts, becomes incandescent under the action of the gas, 

 giving rise to a yellowish liquid, which, on cooling, forms a]mass 

 of a paler colour. 



Iodine, bromine, sulphur, and phosphorus can also combine 

 with thallium to form iodides, bromides, sulphides, and phosphides. 



Recently-prepared thallium retains its metallic lustre in water, 

 which it does not decompose even at the boiling-point ; it is de- 

 composed, however, with liberation of hydrogen when an acid is 

 added. 



Sulphuric and nitric are the acids which most readily attack 

 thallium, especially when aided by heat. Hydrochloric acid, 

 even when boiling, only dissolves it with difficulty. White 

 soluble salts are formed, the sulphate and nitrate, which crystal- 

 lize with facility, and a difficultly-soluble chloride, which, how- 

 ever, also crystallizes. 



The chloride formed by the direct action of chlorine or by 

 aqua regia is deposited from the aqueous solution in the form of 

 magnificent yellow laminae, which appear to belong to the rhom- 

 bohedral system. 



Zinc precipitates thallium from the solutions of the sulphate 

 and nitrate in the form of brilliant crystalline laminae. 



