368 Allen and Crenshaw — Sulphides <f Zinc, 



were present, but both the latter are removed by ammonium 

 sulphide.* 



Any form of mercuric sulphide dissolves readily in concen- 

 trated solutions of sodium (20$Na a S, and 35$ KJS were 

 actually used) or potassium sulphide. If the sulphide of mer- 

 cury is kept in excess, the product is much darker than the 

 vermilion powder formed by ammonium sulphide. The differ- 

 ence is solely one of division. The darker product consists of 

 crystals easily recognized by the naked eye. These, when 

 ground in the mortar, are scarcely distinguishable from the 

 vermilion powder made from ammonium sulphide, while the 

 optical properties as determined by the microscope are identi- 

 cal. The alkali sulphides form with mercuric sulphide two 

 compounds HgS.2M,S and HgS.M a S. The latter, we may 

 mention in passing, is easily formed in long hair-like needles 

 of dark green color, when the alkali sulphide solution is 

 evaporated. Individually developed crystals of cinnabar are 

 formed by the solvent action of dilute solutions of the alkali 

 sulphides on mercuric sulphide. The black amorphous sul- 

 phide is always the first product when mercuric salts are pre- 

 cipitated by alkali sulphides, but on digestion with the latter 

 at 100°, it gradually passes into cinnabar. Much interest 

 attaches to the fact that cinnabar only is obtained from these 

 alkaline solutions. (See p. 380.) Numerous experiments were 

 made with mercuric chloride and dilute solutions of sodium or 

 potassium sulphide or polysulphide between 100° and 200°. 

 The experiments were made in sealed tubes and were con- 

 tinued several days. Many of the experiments were discon- 

 tinued before the amorphous black sulphide was all crystallized, 

 but nietacinnabar was never observed and cinnabar was always 

 found. 



Effect of sublimation on Vermilion, HgS. 



When the red powder which is formed by the action of 

 ammonium sulphide is sublimed in an evacuated glass tube, 

 the sublimate is quite black. If the layer on the walls of the 

 tube is very thin, i. e. was cooled with sufficient rapidity, it is 

 entirely black, but in thick layers the product is practically all 

 coarsely crystallized cinnabar coated with a thin layer of the 

 black sulphide. Whether this coating is amorphous or crystal- 

 line metacinnabar, it is impossible to say. Ground in a mortar 

 the product is liver-colored like some ores of mercury. If, 

 now, the ground sample is treated with a few cubic centi- 



* The original amorphous sulphide always left a small residue of metallic 

 mercury when the sulphide was dissolved by sodium or potassium sulphide 

 solution, while the red product formed from it showed none when treated 

 in the same manner. The chlorine in the original product volatilized as 

 mercuric chloride when heated in an evacuated glass tube. 



