272 milehrand and Schaller — 3/> rcury 



habits, one determined by the development of the rhombic 

 dodecahedron and not particularly rich in forms, the other 

 determined by development of the octahedron and with abun- 

 dant forms. Of the 21 forms observed 17 are new. Whether 

 eglestonite can be distinguished by its color in the mine or soon 

 after removal therefrom from terlinguaite, with which it is 

 sometimes closely associated, or from kleinite or the orange 

 montroydite, we are unable to say, but from the confusion that 

 existed in the minds of those who sent us our specimens it seems 

 that it must be at least difficult to do so. The first specimens 

 received were dark brownish and of dodecahedral habit, others 

 were of octahedral habit and light brownish yellow. These 

 last became darker in time. If sufficiently exposed the crys- 

 tals turn black, but without losing their luster, as noticed by 

 Moses. Streak yellow, turning black. Luster adamantine to 

 resinous. Transparent to translucent. Brittle. Cleavage lack- 

 ing. Fracture uneven and apparently sometimes conchoidal. 

 Hardness, 2-3 (Moses). Density, 8*237 (Moses) ; not determined 

 by us for the same reason as with terlingnaite, difficulty of 

 freeing perfectly from mercnry enough material for a satisfac- 

 tory test. 



When heated in a closed tube comports itself in almost every 

 respect like terlinguaite. The residue, after expulsion of the 

 calomel, seems to be mercuric oxide as with terlinguaite, 

 formed in this case, however, from mercurous oxide at the 

 expense of half the mercury of the latter, a reaction which 

 accords with the observation that no oxygen escapes till all the 

 calomel and some mercury have sublimed. 



Hydrogen sulphide acts very much as upon terlinguaite and 

 ammonia blackens at once, the latter reaction serving as a ready 

 distinguishing test between the two minerals. Hydrochloric 

 and nitric acids decompose it with separation of calomel. The 

 hydrochloric acid filtrate contains no mercury. Cold dilute 

 acetic acid acts more quickly on the powder of eglestonite than 

 on that of terlinguaite, calomel is left and from the filtrate 

 much more can be obtained by hydrochloric acid. The final 

 filtrate is free from mercury. These tests, confirmed by the 

 analysis, show clearly the mercurous nature of the compound, 

 the first authentic instance of a mercurous oxychloride, native 

 or artificial. 



Analysis did not confirm the empirical formula Hg 6 Cl 3 2 , 

 deduced from J. S. McCord's analyses in the paper by Professor 

 Moses, a formula which, in fact, is invalidated by the qualita- 

 tive data above given, since it calls for mercuric as well as mer- 

 curous mercury. The analyses were made in the main as for 

 terlinguaite, with the exception that the chlorine and mercury 

 in the sublimate were each time determined, the separation 



