80 



metallic mercury. The spirit solution, digested on mercury, with 

 occasional shaking, produces the black sulphide of mercury, while 

 the aqueous solution, similarly treated, produces the red sulphide. 

 Insoluble sulphides, however, exist in the foul clay, and evolve sulphide 

 of hydrogen on the addition of an acid. These insoluble sulphides 

 are oxidized rapidly by exposure of the clay to atmospheric action. 



A solution of clay in spirit was treated with an excess of powdered 

 acetate of lead, and the white precipitate filtered off. The brown 

 filtrate was supersaturated with ammonia and filtered. The clear 

 brown filtrate, diluted with twelve times its bulk of water, became 

 milky, and with much difficulty was obtained clear by filtration. 

 Part of the spirit was then distilled off, to ascertain whether it would 

 bring over a volatile sulphur compound, but the spirit was quite free 

 from sulphur. The remaining fluid was then acidified with nitric 

 acid, which caused brisk effervescence and a strong smell of hydro- 

 cyanic acid. Nitrate of silver was added as long as it continued to 

 produce a precipitate ; the precipitate, dried and heated, gave off 

 cyanogen, which burnt with its characteristic flame. The clear fil- 

 trate, slowly evaporated to dryness, left a pale yellow crystalline mass, 

 which did not change colour by several days' exposure to light. Part 

 of this, burnt in a porcelain crucible, gave off nitrous fumes, and left 

 a considerable residue blackened by oxide of silver. Water was 

 added to this residue, and the oxide of silver filtered off, and an 

 abundant precipitate of sulphate of baryta obtained, with a salt of 

 baryta. The remainder of the yellow salt was redissolved in water, 

 with a view to separate a granular portion which was mixed with the 

 more perfectly crystalline salt, but an accident unfortunately spoilt 

 the remainder, and rendered any further progress impossible. 



Sulphocyanide of ammonium may be obtained in considerable 

 quantity from an alcoholic solution of foul clay. Upon one occasion 

 I obtained nearly an ounce, in a fair state of purity, from less than 

 a quart bottle of foul clay ; and so tenaciously does clay retain this 

 compound, that from some clay which had been exposed to the full 

 action of the weather in a field for two years, I obtained a consider- 

 able coloration with perchloride of iron. Sulphocyanide of ammo- 

 nium may be obtained from gas which has been purified by oxide of 

 iron, by passing the gas through spirit of wine and evaporating. 



When common yellow brick-clay is used in the purification of coal- 



