Intelligence and Miscellaneous Articles. ^11 



quantity unknown to the analyst. As the different weights agreed 

 with the original weight of the mineral I had given out lor analysis, 

 no error could have crept into the result. — Poggendorff's Annalen, 

 No. 10, 1838. 



ON THE COMPOSITION OF IDOCRASE FROM SLATOUST. 

 BY F. VARRENTRAPP. 

 Klaproth, von RobeU, and particularly Magnus, have shown, after 

 verj' careful analysis, that idocrase and garnet have the same che- 

 mical composition. Notwithstanding that every attention has been 

 directed to find an essential chemical difference to account for the va- 

 riation in the crystalline form, it has been hitherto in vain. Ivanor's 

 analysis, as reported in the Transactions of the St. Petersburg Aca- 

 demy, of an idocrase from Slatoust in Siberia, has attracted attention, 

 as the result is not in accordance with that of other chemists, and 

 the difference is such as to require a different formula. The locality 

 was the same as the idocrase examined by Magnus. G. Rose having 

 brought a quantity of this mineral from Siberia, Mr. F. Varrentrapp 

 repeated the analysis, with the following results : 



Varrentrapp. Magnus. Ivanor. 



Silica 37-55 37178 37079 



Alumina 17-88 18-107 14-159 



Lime 3556 35-790 30-884 



Protoxide of iron.. 6-34 4-671 16017 



Magnesia 2-62 2-268 1-858 



I 



99-95 98-024 99-997 



The mineral consisted of well-formed transparent green crystals 

 imbedded in felspar, from which they were easily separated, exactly 

 the same as those described by Magnus in his analysis. The cry- 

 stals were carefully selected, reduced to fine powder, heated with car- 

 bonate of soda, and examined in the usual manner. The great dif- 

 ference in the results between M. Varrentrapp and M. Magnus on 

 the one side, and M. Ivanor on the other, is difficult to account for. 

 It may have arisen in M. Ivanor's analysis in the use of too small a 

 quantity of potash in the separation of the alumina from the oxide 

 of iron, which would give a larger proportion of oxide of iron and a 

 smaller one of alumina ; the deficiency in the quantity of lime may 

 have arisen from not having quickly enough filtered the solution 

 after precipitating by ammonia. 



Fuchs observed as long ago as in 1818, that idocrase, as well as se- 

 veral other minerals containing an alkali or an alkaline earth, when 

 subjected to a strong heat and fused, were capable of being decom- 

 posed by hydrochloric acid, forming a gelatinous mass. Von Robell 

 and Magnus confirmed this observation, and the latter further ob- 

 served that the specific gravity of idocrase after fusion was con- 

 siderably diminislied, although no altenitiou in the composition could 

 be discovered. 



M. Varrentrapp in making a second analysis of tliis mineral first 

 fused it ; he obtained a good flowing clear glass of a brown colour, of 



