348 CHEMICAL EXAMINATION OF MINERALS 



Since the residue appeared to contain impurities in the silica, dilute sulphuric acid was 

 added, and the whole evaporated until acid fumes began to be evolved. After cooling, 

 water was added, and the silica separated by filtration. To the filtrate was added am- 

 monia and hydrosulphuret of ammonium, the zirconia and sulphuret of iron, after settling, 

 removed by decanting and the iron separated from the zirconia by sulphurous acid accord- 

 ing to Berthier's method. The zirconia was, after boiling, filtered and washed, and after 

 decomposing the sulphites and hydrosulphites by nitric acid, the iron was separated from 

 the filtered liquid by ammonia. The addition of phosphate of soda to the filtrate from 

 the oxide of iron, and suffering the beaker to stand in a warm place for several days, gave 

 negative results as to the presence of magnesia. The silica in this analysis was treated 

 twice by concentrated hydrofluoric acid, (which was pure, leaving no residue when evapo- 

 rated,) and a residue was obtained which, after heating with sulphuric acid weighed 0-038. 

 On boiling this with dilute sulphuric acid to the evaporation of part of the acid, 0-0095 of 

 zirconia was obtained, and 0-0075 silica, which together equal 0-0 17, leaving unaccounted for 

 0-021, possibly soda or its salt, in combination with the silica and zirconia. Subtracting 

 the zirconia from the silica, and adding it to that already obtained, this first analysis on 

 one gramme, gave the following per centage results: — 



Silica, . . . 36-72 



Zirconia, . . . 65-45 



Peroxide of iron, . . 2-07 



Water, . . . 0-50 



104-74 



Both silica and zirconia are here evidently too high. The former two per cent, from 

 the probable presence of alkali; the zirconia also two per cent., from a cause to be men- 

 tioned later. 



The difficulties presenting themselves in the analysis of zircon are owing, as is well 

 known, to the facility with which its zirconia forms insoluble compounds with silica, and 

 the re-agents necessary to effect its separation. From my experiments on this mineral it 

 would appear, that even the low temperature of the steam bath when water is absent, has 

 a tendency to the formation of basic zirconia compounds, not readily soluble even in sul- 

 phuric acid. On the supposition that this would not take place by presence of sulphuric 

 acid in considerable excess before evaporating to dryness, and that its silica would be, 

 perhaps, rendered insoluble by the same temperature, I modified its analysis in the fol- 

 lowing manner, which would appear to be a speedy and accurate method for the analysis 

 of zircon. One gramme of the elutriated mineral, after determining the water by igni- 

 tion, was fused with four times its weight of carbonate of soda without addition of nitre. 

 Ten minutes' exposure to the heat obtained by forcing a current of air by the table 

 blowpipe through a gas argand flame was sufficient to effect a complete decomposition. 

 To the residue was added a considerable quantity of water, then hydrochloric acid in the 

 cold, without first separating the granular zirconia soda as proposed by Scheerer. The 

 silica remains as pure white flocculse without any grit. An excess of sulphuric acid is 

 now added and the whole evaporated until fumes of the acid are evolved, at which tem- 

 perature it is kept for some time. It would lie, perhaps better to add sulphuric acid at 



