Minerals from Terllngua, Texas. 271 



In vacuo the color changes of the crystals as the heat increases 

 are more marked, these being, after first appearance of a sub- 

 limate, red, black (without loss of luster), red-brown, orange- 

 brown and dull. Before becoming completely orange-brown 

 some faces are olive-green. When orange-brown the only 

 visible sublimate is calomel and no trace of oxygen has been 

 evolved. The residue then seems to be mercuric oxide, upon 

 the decomposition of which partial recombination of its con- 

 stituents occurs, to judge from the deposition on the warm 

 glass near by of a slight orange-brown sublimate. 



Hydrogen sulphide blackens the edges of a crystal, but fur- 

 ther action is very slow ; ammonia blackens only after some time. 

 The second test serves to distinguish the mineral from eglestonite, 

 which is at once blackened by ammonia. This difference in 

 behavior of terlinguaite and eglestonite is in line with their 

 chemical difference, the former being mercuric-mercurous. the 

 latter wholly mercurous. Hydrochloric and nitric acids decom- 

 pose terlinguaite with separation of calomel. The hydrochloric 

 filtrate yields much bivalent mercury. Cold acetic acid slowly 

 decomposes the mineral when in powder, also with separation 

 of calomel, and in the filtrate hydrochloric acid produces no fur- 

 ther precipitate, or but a very faint one. Eglestonite under 

 similar treatment yields a heavy calomel precipitate, the filtrate 

 from which is free from mercury. 



Moses' empirical formula was confirmed by analyses in 

 which the oxygen was measured directly and found to be wholly 

 absorbed by phosphorus, thus showing its freedom from 

 nitrogen. 



Analyses of terlinguaite calculated to gangue-free substance. 

 Theory Eatio 



Hg 2 C10 I II III of III 



Hg 88-65 88-92 88-31 88-61* 2-00 



CI 7-85 7-83 I'OO 



O 3-50 3-75 1-06 



10O-00 100-19 



The high oxygen found in III is due probably more to error 

 in measuring so small a volume as 2-67 cm3 than to the little 

 montroydite that was present. 



The only artificial mercuric-mercurous oxy chloride hitherto 

 preparedf has the formula of terlinguaite. 



^Eglestonite. 



Isometric-holohedral. Crystals small, equidimensional, usually 

 about and under one millimeter in diameter. They show two 



* Mean of I and II. 



•f Fischer, T., and von Wartenberg, H. Chern. Zeit., xxix, 308 (1905). 



