THALLIUM. 



acted on by hydrochloric acid, rapidly by nitric and sulphuric, differ- 

 ing in this respect from lead. The metal is quite soft, and can be 

 even scratched with the nail, when precipitated from its sulphate or 

 nitrate by means of zinc, it forms crystalline plates. "When thallium 

 solutions are decomposed by electricity, brown peroxide is precipitated 

 in which respect again it resembles lead, but the deposited oxide dis- 

 solves again. 



The equivalent appears to be 204 ; this fact cannot be taken as any 

 argument against the propriety of ranking thallium among the alkalic 

 metals, as the equivalents of lithium, sodium, potassium, rubidium and 

 coesium are respectively 7, 23, 39, 85, 123. The position of the 

 bright green thallium line does not correspond with any dark line of 

 the spectrum, and hence we may conclude that this new element does 

 not exist in the solar atmosphere. 



By electrolysis it can be obtained in beautiful metallic crystals; 

 which if required in mass, can be squeezed and fused under cyanide of 

 potassium. It is very malleable, but not very ductile, wires must be 

 formed by squeezing the metal through tubes. The specific gravity 

 is 11.9, which would certainly tend to separate it from the alkalic 

 metals. The metal will mark paper like lead, but the marks soon be- 

 come obliterated from the formation of the oxide, they may be repro- 

 duced by washing with sulphide of ammonium, when black sulphide 

 of thallium is formed, which however also oxidises rather readily to 

 sulphate ; another point in which there is a certain resemblance to 

 lead, and not to potassium. 



Thallium may be ranked next to bismuth, as regards its diamagnetic 

 properties. 



It fuses at 550 F. (287 C.) and distils at a red heat. The crust 

 formed on the metal by exposure is first yellow and then becomes dark» 

 easily removed by water, and communicating to it a strong alkaline 

 reaction, and a caustic biting taste. Owing to the same cause, the 

 metal makes marks on turmeric paper, which soon become brown. 



As regards its power of conducting electricity, thallium stands be- 

 tween lead and tin, the relative powers being respectively 7.77, 8.64, 

 11.45. 



Quantitative Determination. If the thallium is present in the form 

 of protoxide, it can be precipitated from its solution by bichloride of 

 platinum, but this method is objectionable, inasmuch as the yellowish 

 white double chloride is in such a fine state • of division as to pass 



