364 Pfof. Stromej'er's Analyses 



The analysis of the olivine by Klaproth, therefore, states the 

 oxide of iron and the silica contained in this fossil much too 

 high, and on the other hand the quantity of the magnesia at 

 least 12 per cent too low. From the process pursued by 

 this chemist, it is easy to perceive how so considerable a pro- 

 portion of magnesia might have escaped him, and how the 

 silica and oxide of iron must thereby have appeared so much 

 the greater in quantity. 



According to the experiments of the same chemist, some 

 lime is also contained in olivine. But neither in the olivine 

 from the Vogelberg, nor in that from Casalthof in Bohemia, 

 was there any trace of it ; and as this substance was in vain 

 sought for in many other olivines also, and particularly in that 

 from the Habichtswald at Cassel, whence that examined by 

 Klaproth was brought, it may very well be assumed that the 

 lime obtained by him resulted from the mixture of another 

 calcareous mineral accidentally with this, or perhaps might 

 have arisen from the filtering paper, which at that time it was 

 not customary to purify previously by acids. 



The discovery of oxide of nickel in olivine is a new fact, 

 which, notwithstanding the small quantity in which this me- 

 tallic oxide enters into the composition of the mineral, is still 

 of importance in regard to its origin. As the presence of oxide 

 of nickel in olivine had not till now been observed by any che- 

 mist, the suspicion at first naturally arose that it was contained 

 merely accidentally in the olivines submitted to this specific ex- 

 amination. But experiments which on this account have been 

 made with many other very pure olivines, brought fi-om very 

 different parts, (as for example, wnth that of the Habichts- 

 wald, that from the Eifel, from Vesuvius, fi-om Rantieres at 

 Ardes in Auvergne,) leave no doubt of the constant presence 

 of oxide of nickel in this mineral. 



The quantity of oxide of nickel found in olivine now in- 

 duced the suspicion of the presence of oxide of chrome in it 

 also ; but neither by treating it with nitre, nor by dissolving 

 it by means of caustic alkali, could any trace of this metallic 

 oxide be detected. 



The iron occurs in the olivine, as is already mentioned, in 

 the state of protoxide ; and by no means as black oxide of 

 iron, as is assumed by Klaproth. However, there is still 

 found in it also a slight mixture of this metal in the state of 

 black oxide. To this, olivine owes its pale yellowish-green. 

 By continued ignition, with the admission of the air, this 

 combination passed to black oxide of iron ; and then it dis- 

 plays similar variegations of colour to those of iron window 

 frames, where this phaenomenon also proceeds from an in- 

 creased 



