76 Intelligence and Miscellaneous Articles. 



This property it possesses in common with selenium. If the tellu- 

 rium is allowed to cool slowly, the air usually penetrates the upper 

 surface, and in the centre there is a large cavity, from around which 

 fragments may be taken that contain none. The mean of six trials 

 gave M. Berzelius 6-2445 as the specific gravity ; and he found the 

 atomic weight to be 802- 121. 



Tellurium combines with two proportions of oxygen to form tel- 

 lurous and telluric acid: the former is already known as oxide of 

 tellurium. It has two isomeric modifications : one of them is pro- 

 duced at a moderate heat, and the other by the actions of the al- 

 kalis upon it. Berzelius distinguishes them by the letters A and B : 

 the latter differs from the former in dissolving readily in acids, in 

 ammonia, and the alkaline carbonates, from which it expels the car- 

 bonic acid. Tellurous acid forms peculiar salts; but M. Berzelius, 

 at present, knows only those formed by the modification B. They 

 are of various degrees of saturation, that is to say, they contain an 

 atom of base, combined with 1, 2 and 4 atoms of acid : the last are 

 most readily formed ; those with alkaline bases crystallize. 



Telluric acid is very imperfectly formed in the humid way with 

 aqua regia ; but it is produced in the dry way, by treating tel- 

 lurous acid with nitre. That it has not been before discovered, is 

 owing to the circumstance that the tellurate formed offers an unex- 

 pected isomeric modification, and is partly transformed into tellu- 

 rite, when too strongly heated. The following is the best method of 

 preparing telluric acid: Fuse a mixture of equal parts of potash and 

 tellurous acid : dissolve the salt in water, and add hydrate of potash 

 equal in quantity to that employed, or rather more : pass a current 

 of chlorine into the liquor, until the turbidness and precipitate at 

 first occasioned are redissolved, and the liquor smells of chlorine. 

 Add a little muriate of barytes, and filter if any precipitate be 

 formed; this is either sulphate or seleniate of barytes: then pour 

 ammonia into the solution, until it is slightly in excess, and preci- 

 pitate the tellurate of barytes [potash?] by muriate of barytes. The 

 precipitate is at first bulky, but soon becomes granular and falls to 

 the bottom of the vessel: if this does not occur it is because it con- 

 tains tellurite of barytes. The salt is then washed, and digested with 

 a quarter of its weight of concentrated sulphuric acid previously di- 

 luted with water: filter the liquor, evaporate the greater part of it in 

 a salt-water bath, and afterwards spontaneously : the acid crystal- 

 lizes in fiat hexahedral prisms, terminated by a flat four sided pyra- 

 mid. When the sulphuric acid is in excess, the crystals are more 

 perfect : this acid may be removed by concentrated alcohol. 



In this state telluric acid contains 235 per cent, of water, which 

 it retainsat212°; at a higher temperature, but below redness, it loses 

 two thirds of the water, without destroying the crystalline form : 

 the acid is then difficultly soluble in water, but it gradually dissolves 

 by long boiling. At a high temperature it loses the last third of its 

 water, and there then remains a lemon yellow powder, which is inso- 

 luble in any fluid : it is an isomeric modification of telluric acid, cor- 



