4 Analysis of the Chromates of Iron 



fracture is lamellar, and not granulated ; its metallic bril- 

 liancy is more vivid, and it evidently contains a smaller 

 admixture of earthy matters. The specimen in my pos- 

 session shows spots of green on some parts of its surface, 

 which are discovered to be oxide of chrome. The spe- 

 cific gravity of the two also serves to support my conjecture 

 regarding them. That of my specimen is 4-0579, while 

 the specific gravity of the mineral of Var is only 40326. 

 This difference in weight necessarily makes a difference in 

 the proportions of the metallic part of the two chromates; 

 and, as wo shall presently see, the analysis agrees com- 

 pletely with this physical property. 



Chemical Examhiat'wn. 



1. When strongly calcined it loses about 1-lOOth part of 

 its weight, and acquires a reddish brown colour. Having^ 

 placed 100 parts of this mineral reduced to an impalpable 

 powder, together with 300 parts of pure potash, in a cruci- 

 ble of platina, I exposed the whole to a strong heat. The 

 mass, when removed from the fire, and nearly cooled, was 

 in part of a green and in part of an orange colour. The 

 water which I added to it assumed a rich citron yellow, 

 exactly similar to the colour of chromate of potash. When 

 the mass no longer gave a tinge to distilled water, I digested 

 it in very weak muriatic acid, with the intention of sepa- 

 rating what part of the oxide of iron had been set free by 

 the action of the potash, without touching, in any degree, 

 the chromate of iron, which was still undecomposed. I 

 now washed the remaining substance again, till the water 

 came off insipid, and a second time melted it with a portion 

 of pure potash. 



In this wav I heated the mineral six different times, al- 

 ternately with potash and muriatic acid ; setting aside the 

 alkaline and acid solutions, that I might examine them se- 

 parately. 



The residuum consisted of a brownish gray matter, 

 weighing 090 : niuriatic- acid took up from it a little iron, 

 and the remainder was completely dissolved in nitro-muriatlc 



acid. 



