Hardman and Hull — A HitheHo Undescrihed Mineral. 163 



Sonstadt's solution is a solution of mercuric iodide (or red iodide) 

 in potassic iodide — the liquid being concentrated by adding, alter- 

 nately, the mercuric and the potassic iodides until no more of either 

 is taken up. Carefully proceeding in this way, a clear liquid can be 

 obtained, having a specific gravity of a little over 3'00, according to 

 Sonstadt and Church. It is clear that any mineral of less specific 

 gravity than 3" floats on such a liquid, whiie any of higher gravity of 

 course will sink ; by diluting the liquid we can obtain a range of 

 solutions capable of separating any minerals between TO and 3-0 s. g. 

 The Carnmoney mineral being of low specific gravity, a solution of 

 about 2"0 was sufficient. The rock being crushed up and sifted, to 

 get rid of small dust, which would have rendered the result less 

 palpable, was thrown into a dish filled with the solution. Every- 

 thing but the new mineral sank to the bottom. The latter was then 

 iskimmed off, and immediately washed with distilled water to which 

 a little potassic iodide had been added, to dissolve any red iodide 

 which would otherwise be thrown down, and finally washed with 

 distilled water. When a sufficient quantity of the mineral had been 

 thus collected it was again treated in the same way, and thus was 

 cleared of a few particles of augite, &c., which had been caught up 

 in the first floatation. 



In this way about 3 grammes of the mineral were obtained, per- 

 fectly free from admixture, and quite sufficient to yield exact analy- 

 tical results. 



The analysis was conducted in the usual way, by the fusion of the 

 powdered mineral with the alkaline carbonates. Although it appears to 

 be nearly altogether decomposed by boiling (when powdered) in strong- 

 hydrochloric acid, the fusion process seems to be the most complete me- 

 thod, and is the shortest in the end ; because, if boiling with acid is 

 depended on, the insoluble residue will be found almost invariably to 

 contain undecomposed silicates, giving an excess in the amount of 

 silica. 



The ferrous iron was determined according to Early's method, 

 namely, by decomposing the mineral with hydrofluoric acid, and esti- 

 mating the ferrous iron as quickly as possible by means of a standard 

 solution of bichromate of potassium. 



As it was not easy to obtain enough of the mineral to enable its 

 specific gravity to be taken in the ordinary way, its gravity was de- 

 termined in a somewhat novel way. It fioats on, and is hardly affected, 

 even after some months, by strong sulphuric acid of the usual density, 

 viz., 1-84. Dilute sulphuric acid, of the density of the mineral, was 

 prepared, and the specific gravity determined by means of a delicate 

 hydrometer;^ the density by this means was found to be only 1-76, so 



^ Sonstadt's solution might have heen used, hut sulphuric acid \vas found to be 

 more convenient at the time. 



The analysis was performed by me in the Laboratory of the Royal College of 

 Science in Dublin, by permission of Prof. Galloway. 



