216 Professor GmelirTs Analysis of ' Helvine. 



The loss, somewhat considerable, which occurred in both 

 analyses, may be justified partly by the small quantity of the 

 substance subjected to analysis, partly by the difficulty which 

 is met with in the exact determination of the protoxide of 

 manganese. It is, indeed, very probable, that manganese is 

 contained in this mineral in the form of protoxide, because 

 otherwise no such considerable disengagement of sulphuretted 

 hydrogen should take place, when the mineral is treated with 

 muriatic acid. But the oxide of manganese obtained by the 

 ignition of the carbonate had been reckoned black oxide, 

 though under these circumstances a certain quantity of the 

 red oxide might have been formed, in which case, the quanti- 

 ty of manganese would have been underrated. The great 

 quantity of oxide of manganese contained in helvine satisfac- 

 torily explains why the sulphur contained in this mineral 

 had escaped Dr Vogel, because this oxide is superoxidat- 

 ed when the fossil is ignited with potash, whereby the sul- 

 phuretted hydrogen, disengaged by muriatic acid that is pour- 

 ed upon the ignited mass, is immediately decomposed by chlo- 

 rine, which is evolved at the same time. 



The results of these analyses of helvine are such, that this 

 mineral will scarcely be placed hereafter close to garnet. It 

 appears, besides, not to be possible to decide what the chemi- 

 cal composition of helvine may be, when it is considered, that 

 scarcely an analogous composition had been hitherto discover- 

 ed amongst minerals. It might be, perhaps, regarded as a 

 combination of double-silicates of oxide of manganese and 

 glycine, with an oxysulphuret of manganese ; the results, par- 

 ticularly those of the second analysis, are not unfavourable to 

 this view. But I consider this as a mere conjecture, as the 

 rarity of the mineral has hitherto not allowed me to examine 

 it to such an extent as I could have wished. 



