182 Process for dTjeing a fine Mineral Yellow Colour. 



liant yellow colour which can be imagined, and which is not at- 

 tended with the same inconveniences as the preceding, is the sul - 

 phuret of arsenic, or realgar*, which gives also to paint a very 

 lively permanent colour, when care is taken not to associate it 

 with certain metallic oxides, which soon tarnish its brilliancy. 



It is by dissolving this sulphuret of arsenic in ammonia, that 

 I have obtained a liquor fit for dyeing ; but in order that this 

 solution may be effected easily, it is necessary that the sulphuret 

 should be in a certain state of division. To bring it to this state, 

 observe the following process : 



Mix together one part of sulphur, tvvo parts of white oxide of 

 arsenic, and five parts of the potash of commerce; melt the whole 

 in a crucible till it is nearly red hot, and a vellow mass will be the 

 result. Dissolve this mass in warm water; then filter the Hquor 

 to separate it from a sediment formed principally of metallic 

 arsenic in brilliant spangles, and partly of a small quantity of a 

 flocculent matter of a chocolate colour, which appears to be a 

 sub-sulphuret of arsenic. Pour into the filtered liquor a quan- 

 tity of water ; next add some dilute sulphuric acid, which will 

 cause a flocculent precipitate of a superb yellow colour. This 

 precipitate washed on a cloth dissolves with extreme facility in 

 ammonia, and yields a yellowish liquor, to which an excess of am- 

 monia is added to render it colourless. It is in this liquor that 

 the wool, silk, cotton, or flax to be dyed is plunged ; and it is 

 more or less diluted vnlh water, according to the different shades 

 which it is wished to obtain f. It is necessury carefully to avoid 

 making use of metallic utensils. When the stuffs are withdrawn 

 from this bath, they appear colourless ; but insensibly they as- 

 sume a yellow colour as the ammonia evaporates. They are ex- 

 posed to the open air in such a manner that the whole of their 



* I know that generally arsenical preparations inspire a degree of horror; 

 but though the sulphuret of native arsenic, which is often mixed with the 

 oxide of arsenic, may not be exempt from danger, the sulphuret of artificial 

 arsenic obtained by precipitation and well washed, does not appear to me to 

 have any pernicious influence on the animal oeconomy. At least I have ad- 

 ministei'ed it in considerable doses to dogs or cats without their appearing 

 incommoded by it. 



•f It appears that when the sulphuret of arsenic is dissolved in the am- 

 monia a small quar^tity of the arsenic oxidizes ; for if into the liquor there 

 is poured an excess of lime water, a white precipitate of arseniate of lime is 

 produced. This oxidation seems even to keep going on ; iind when a solu- 

 tion sufficiently concentrated of sulphuret of arsenic in ammonia is left to 

 stand for some time, small crystals of arseniate of ammonia are deposited : 

 if an acid is added, it produces a precipitate of sulphuret of arsenic mixed 

 with sulphuret of the oxide of aisenic of a palish yellow. It may be proper 

 therefore not to dissolve the sulphuret of arsenic in ammonia, except in 

 proportion as it may be required. 



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