Dr. Percy on the Composition of Beudantite. 167 



Sesquioxide of iron 2*50 = 37*65 per cent. 



Arsenic by loss 0*59 = 8*88 per cent. =13*60 (As O 5 ). 



Sulphate of baryta 2*40 = 0*82 (SO 3 ) = 12*35 per cent. 



Sulphuric Acid. 



Weight of mineral 5*34 grs. 



Sulphate of baryta 2*00 = 0*69 (S0 3 ) = 12*92 per cent. 



Water, Arsenic and Sulphuric Acid. 

 Weight of mineral 3*54 grs. 

 Loss by calcination 0*40= 11*30 per cent. 

 Sulphate of baryta 0*90 = 0*31 (SG 3 ) = 8*76 per cent. 

 Arsenic by loss 026 = 7*34 per cent. =11-24 (As O 5 ). 



Determination of Sulphuric Acid in another portion of the same 

 specimen as used in the last determination without calcination. 

 Weight of mineral 2*40 grs. 



Sulphate of baryta =0*83 = 0*28 (S0 3 ) = 11*67 per cent. 

 Loss of sulphuric acid in calcination is 1 1*67 — 8'76 = 2*9l 



per cent. 

 Water, therefore, is 11*30 (loss by calcination) — 2*91 (loss 

 of sulphuric acid by calcination) =8*49 per cent. 



I. II. 







Oxygen. 





Oxygen. 



Oxide of lead . . 



. 24-47 



1-75 



29*52 



2-12 



Sesquioxide of iron 



4246 



13*02 



3V65 



11*54 



Sulphuric acid 



. 12*31* 



7'37 



12-35 



7*39 



Arsenic acid . . 



, 9*68 



3*36 



13*60f 



4-72 



Phosphoric acid 



1*46 



0*82 



not dete 



rmined. 



Water . . . . , 



8*49 



7-55 



8*49 



7*55 



98-87 101*61 



The preceding results prove that Beudantite is chiefly com- 

 posed of sesquioxide of iron and oxide of lead, and so far con- 

 firm the accuracy of Wollaston's examination of it. They 

 also confirm Damour's statement of the presence of arsenic 

 and sulphur, and further demonstrate the presence of phos- 

 phoric acid. But the sulphur cannot, as Damour supposes, 

 exist even in part as sulphuret, because the mineral dissolves 

 without residue in hydrochloric acid ; whereas if a sulphuret 

 were present, there would be a residue of free sulphur, the 

 result of the action of the sulphuretted hydrogen evolved by 

 the decomposition of the sulphuret upon the sesqnichloride 

 of iron formed at the same time. 



* Mean of three determinations. 



f I think it probable that this determination of arsenic is very sensibly 

 excessive. I have not given the mean of the several determinations, be- 

 cause I wished to put together the results obtained in the analysis of one 

 portion of the mineral. 



