252 Identity of Edwardsite with Monazite. 



The discrepancy in specific gravity between the two minerals 

 disappears on subjecting larger crystals of Edwardsite to exam- 

 ination. I obtained on a fragment weighing 2^ grs. the specific 

 gravity of 5.00; whereas the Monazite crystal, whose weight is 

 3 grs. equals only 4.61. It will no doubt be a difficult point to 

 establish an exact agreement between the two, since the speci- 

 mens to be examined are not only exceedingly minute, but much 

 entangled with other substances, as mica, tin ore, seschenite, &c. 



After proceeding thus far in the examination, I felt but little 

 hesitation in concluding that the analogy would be found to hold 

 still further, and extend to an identity in chemical composition ; 

 the more so, as 1 distinctly remembered several ambiguous and 

 nearly irreconcilable circumstances in my analysis of Edwardsite. 



All the Edwardsite I could collect by breaking up numerous 

 specimens of the rock amounted to but 5.1 grains. In examining 

 each fragment in order to separate foreign matters prior to pul- 

 verization, I detected one very perfect crystal of zircon, (of the 

 form binotriunitaire, fig. 495 of my Treatise,) which taken with 

 the fact that they have frequently been observed in proximity to 

 the Edwardsite, leads me to attribute in part the zirconia of my 

 former analysis to this source. 



My present object was not so much to determine the number 

 and proportions of the ingredients as to ascertain whether the 

 oxide of lanthanium and thorina are constituents of the mineral. 

 It was heated to whiteness for half an hour, with twice its weight 

 of anhydrous carbonate of soda. The mixture fused into a hard, 

 yellowish gray compact mass, which was treated with boiling 

 water and the insoluble part separated on the filter. 



The alkaline fluid was supersaturated with acetic acid, and pre- 

 cipitated by acetate of lead. The phosphate of lead was ignited 

 and weighed 7.5 grs., which is equivalent to 1.38 grs. phosphoric 

 acid, or 27.04 per cent. 



The insoluble matter from the aqueous solution of the calcined 

 mineral was now treated with nitro-hydrochloric acid, and di- 

 gested for several hours. The insoluble portion was separated, 

 ignited and weighed. It amounted to 2 grs. Its color was red- 

 dish brown. Believing it still to contain oxide of cerium, I sub- 

 jected it to a new calcination with carbonate of soda, in order 

 to its more complete decomposition. It had the desired effect ; 

 for after the digestion of the calcined mass afresh in aqua regia 



