432 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



ammonia was present in many cases. Very small quantities of ammonium 

 carbonate precipitate all the mercur_v from the solutions discussed above at 

 ordinary pressures and at temperatures not exceeding- the boiling-point. At 

 temperatures of 145° or more and corresponding pressures, however, mer- 

 curic sulphide dissolves freely in ammoniacal solutions, but it is repre- 

 cipitated on cooling. The entire absence of cinnabar from the original 

 surface of Sulphur Bank shows how complete this precipitation must be 

 and that a "quantitative" separation of mercuric sulphide has there taken 

 place (see page 269). 



Solubility of Fes' — The sulpliidc which is most frequently associated with 

 cinnabar is pyrite or marcasite ; indeed, these minerals in greater or smaller 

 quantities are to be found in nearly every hand specimen of ore and occur 

 very abundantly in most quicksilver mines. It seems impossible to avoid 

 the conclusion that the iron sulphides are soluble in the same natural solu- 

 tions which cany cinnabar. Pyrite, however, is a mineral which is so 

 refractory to most chemical solvents that neither Dr. Melville nor I felt anj'- 

 confidence that sodium sulphide would attack it. On making the e.xperi- 

 ment I was accordingly surprised to find that pyrite, marcasite, or precipi- 

 tated ferrous sulphide, when warmed with a solution of sodic sulphide, 

 diminished in quantity, while the solution changed color. The filtrates gave 

 strong reactions for iron. 



Pyrite dissolves in cold solutions of sodium sulphide without any evo- 

 lution of gas. Ten cubic centimeters of an irreproachable solution of sodic 

 sulphide containing 1.0955 grams of the alkaline sulphide dissolved six- 

 tenths of a milligram of pyrite at the ordinary temperature of the laboratory. 

 Thus over eighteen hundred parts of sodic sulphide are required to dissolve 

 one part of pyrite. The solvent power seems to increase with the tempera- 

 ture. Pyrite, like cinnabar, appears to be totally insoluble in cold sodium 

 sulphydrate, and, like cinnabar, pyrite dissolves to some extent in hot solu- 

 tions of the sulphydrate. Pyrite is also soluble in solutions of sodium car- 

 bonate partially saturated with h3-drogen sulphide, both hot and cold. A 

 solution of 407 parts of the nentral carbonate, after being semi-saturated with 

 hydrogen sulphide, dissolved one part of pyrite at the ordinary temperature 

 i)f the lal)t)rat()r\-. The mineral dissolves more easilv in liot solutions than in 



