112 Mr Magnus's Analysis of Picrosmine. 



obtained by ignition, and to determine immediately its ratio to 

 the other ingredients; nor could I, for the same reason, deter- 

 mine the loss which the mineral might sustain in a higher de- 

 gree of incandescence. 



The following table shows the results of the analysis : — 



Silica, - 54.886 containing oxygen 28.389 



Magnesia, ... 33-348 12.909 



Alumina, - 0.792 0.367 



Peroxide of iron, - - 1.399 0.429 



Protoxide of Manganese, 0.420 0.092 



Water, ... - 7.301 6.490 



98.146 



The oxygen contained in all the bases together, is 13.797, 

 nearly equal to half the quantity of oxygen in the silica ; pi- 

 crosmine, therefore, appears to be a bisilicate of magnesia. I 

 must observe here, however, that I do not consider the speci- 

 men subjected to analysis as entirely pure, since it contained 

 throughout its mass small brown dendritic specks, from which, 

 perhaps, may originate the oxide of iron and the alumina in 

 the analysis, for it is not likely that so small a quantity of a 

 substance not isomorphous with the rest of the bases, should 

 form an essential ingredient in the composition of the mineral. 

 The brown colour of the intermixed substance induced me to 

 consider the iron to be contained in the mineral as peroxide 

 and not as protoxide. But I believe the manganese to be con- 

 tained in it as a protoxide ; because it is thus very frequently 

 found along with magnesia, with which it is isomorphous, and 

 with which it also agrees in many of its chemical properties. 

 The mineralogical formula, in the method of Berzelius, in re- 



ference to the solid ingredients, will be — j S" 2 , or if we ne- 

 glect the small quantity of manganese, it will be MS 2 . 



If we consider all the volatile ingredients as water, their 

 contents of ozygen, equal to 6.49 will form exactly one-half 

 of 12.999, which is the quantity of oxygen in the bases, ex- 

 cluding the oxide of iron and the alumina as accidental ingre- 

 dients. The formula of the whole is then transformed into 

 2MS* + Aq. 



11 



