( 603 ) 
compounds TeS 2 and TeS 8 are present in the brownish-black preci¬ 
pitates, formed when passing H 2 S through solutions of tellurites and 
tellurates. He arrived at that conclusion on account of the solubility 
of these precipitates in aqueous potassium or sodium hydroxide, which 
is also the case with TeO, and TeO a . 
Becker 1 ) was the first to analyze these precipitates and he finally 
arrived at the conclusion that their composition actually corresponds 
with TeS 2 and TeS,. He proved however, that nearly all the sulphur 
may be removed from these substances by treatment with carbon 
disulphide: TeS a yielded a residue containing 6.14 % of sulphur 
instead of 42.85 %, TeS 2 a residue containing 3.69 # / 0 instead of 
33.4 %. He concludes that the black precipitates are only mixtures 
whose composition agrees nearly with those of the supposed com¬ 
pounds According to him they are formed primarily as ephemeral 
compounds, which are at once decomposed by the solvent. Berzelius 1 ) 
and Oppenheim *) obtained double sulphides to which they assigned 
the formulae 3K 2 S + TeS s , etc. In more recent times, BRAUNER 3 4 5 )and 
Gutbier s ) again inclined to the opinion that we are dealing here 
with mixtures Of the elements. 
§ 2. Since Dumas placed tellurium in the sulphurgroup, as the 
first homologue of selenium, and thus the well-known difficulty as to 
the position of tellurium, in regard to iodine, in the periodic system 
introduced later, was created, — the question as to the relation of 
tellurium on the one side and sulphur and selenium on the other 
has again become of actual importance. For now it is undoubtedly 
certain that the atomic weight of tellurium is 127.6 and therefore 
greater than that of iodine. On the other hand the differences between 
tellurium and the other two elements are so strongly pronounced 
that Retgers on account of the isomorphism between tellurates and 
osmiates, thought it would be better to include tellurium in the group 
of the platinum metals. Tellurates to wit, are not isomorphous with 
sulphates, selenates, manganates, ferrates etc. On the contrary, Pellini 
showed an isodimorphisin in the case of (C,H s ) 2 SeBr 2 and (C 4 Hj 2 TeBr 2 , 
whilst Norris and Mommers noticed a direct isomorphism between 
the selenium- and tellurium double chlorides and bromides of dimethyl- 
3 ) Becker, Lieb. Ann , d. Ghem. 180. (1876). 257. 
*) Berzelius, Traite de Chhnie. (1830). 
3 ) Oppenheim, Joum. f. prakt. Ghem. 71. (1857). 270 
*) Brauner, Joum. Ghem. Soc. 67. (1895). 527. 
5 ) Gutbier, Berk Ber. 34. 2114. (1901). 
