ON PREPARING PURE BARYTE8. £3 



The blue colour of the fossil appears to be owing to the Blue colour 



degree of oxidation of the iron ; and this is so much the more owin g toa11 



... ■»« ' ~,-r»." ' ', . *. _ oxide of iron, 



probable, as Mw Hitter has announced the existence of a 



blue oxide of iron. 



Jt is true Mr. Guyton has discovered also a blue sulphuret Not asulphu- 



of iron, to which he ascribes the colour of lapis lazuli: but re * as Guytoti 



in this case perhaps the sulphur may serve to produce this su ^ gse * 



minimum of oxidation. Besides, direct experiments on the 



lazulite have convinced the author of this memoir, that 



it does not contain the least trace of sulphur or sulphuric 



acid. 



VIT. 



On the Preparation of pure Barylcs : by Mr. Robiquet*. 



N a note inserted in No. 183 of the Annales de Chimie, Mr ^'Arcet*- 

 [see Journal No. 76, p. 66], on the decomposition of acetate process for ob- 

 of barytes by means of soda, Mr. d'Arcet points out as a ^"^ J^ e 

 more economical and certain process for procuring pure ba- preferable to 

 rytes, to decompose any barytic salt, particularly the mu- e conaraon ' 

 viate, by a caustic alkali. I conceive however, that the pre- 

 ference he gives to this process over that more generally 

 employed, namely the decomposition of the nitrate by means 

 of heat, is not well founded. 



If we consider the subject in an economical view, we find Comparison of 

 in both cases a soluble barytic salt is first to be formed: that lhera * 

 in the first case we cannot employ liquors sufficiently con- 

 centrated, to prevent any barytes from remaining; in a state Losses in his 



. way, 



of solution: that whatever precaution we take in preparin°* 



the caustic alkali by means of lime, a portion will always 

 become carbonated, were it only during the processes of fil- 

 tration ; consequently there will be so much to be deducted, 

 from the quantity of barytes that might have been obtained : 

 that besides, as the liquor must be shaken during the preci- 

 pitation, a certain portion will then become carbonated : that 

 a loss is occasioned by the washing likewise : and lastly, that 



» Annales de Chimie, Vol. LXII, p. 61^ April, 1807. 



a great 



